By proposing new trade rules, I hope that what was until now the most boring part of the game can be interesting too. It's too bad that trade is there, almost interesting to play, and yet nobody uses it. Sending merchants should really be as exciting and powerful as sending explorers, settlers or armies.
Not controlling the merchants/explorers/settlers, while certainly more accurate and thus a considerable temptation, would not be quite as fun. This is an historical game after all, not a hands-off simulation. (Or else, the only game interface would be to speak to various people, and the game would not last four centuries!) Moreover, for each of those types, a sound argument can be made that kings could direct them when they really wanted to: Louis XIV sent the «*Filles du Roi*»*to help settle New France, a lot of explorations (Drake, Vasco da Gama, even Columbus) were directed at a specific passage, and merchants were also directed (the various Companies that were created by royal assent are a good example!), the Darien Scheme also fits (btw, this is funny that it does not appear in AGCEEP!).
If we want to make it a bit more random, some stupid idea would be that explorers/conquistadors, when sent to an unexplored province, would have instead some random chance of going the wrong way (in another unexplored province, or even turned back by a storm!). After all, even though they had some precise orders, the weather ruled supreme. I'd like it to be tied to the Manoeuver stat; Explorers could also be ordered to make landfall to discover a land province. This could also apply to settlers: they could get lost on their way, and mistakenly settle in the wrong province (wasn't the Mayflower Virginia-bound?). But I fear that this could become really aggravating.
I definitely agree with tying some possibilities with tech. The fact that the infra/trade techs don't have any «*goodies*» after level 4 or 6 has always been a big disappointment. As far as choosing the level goes, I would try and match this to history; so the «*force embargo*» diplomatic action should require about infra 8-10. Likewise, high trade level should enable some blockade-running to be done: for example, a blockaded province should maintain a portion of its trade value, and blockade should not be as efficient for sieges (or you would need a larger fleet). I think this was done in the American independence war, but not much before; correct me if I'm wrong. And since trade research represents the capabilities of merchant ships, this is certainly the good tech to tie blockade-running to.
And a couple extra ideas.
* The Manoeuver stat is a bit useless right now (except for attrition). It could be used for the first assault in a battle (thus being more important in rugged terrain, which seems fine since a plain like Waterloo doesn't help the good manoeuvering generals!). Some of the greatest victories of the time period were done by manoeuvre alone (Frederick II at Rossbach, Napoléon at Ulm). This could also be used to hide your real army strength (again, Frederick and Napoléon played this game a lot).
* As we all know, the number of troops in sieges is a bit wrong. Maybe a high fortress level shouldn't increase much the numbers needed to siege a province, while it could give a better advantage to the defending garrison in an assault, thus effectively requiring a bigger army to successfully assault it. (This is obviously linked to the above-mentioned blockade-running). The bonus to the garrison should be additive and not multiplicative, so that it accurately gets proportionally less interesting as technology improves (a medieval castle is useless against artillery, and Vauban fortifications were going out of style in Napoléon's time). This could even be more detailed: each time you make an assault, you have a chance of taking *some part* (bastion, half-moon, ...) of the fortifications. When you have taken enough, the city is yours. (Think of Orléans before Joan of Arc: the English have a well-started siege since they hold some of the towers). This would make sieges a bit more climactic, which is always good.
Not controlling the merchants/explorers/settlers, while certainly more accurate and thus a considerable temptation, would not be quite as fun. This is an historical game after all, not a hands-off simulation. (Or else, the only game interface would be to speak to various people, and the game would not last four centuries!) Moreover, for each of those types, a sound argument can be made that kings could direct them when they really wanted to: Louis XIV sent the «*Filles du Roi*»*to help settle New France, a lot of explorations (Drake, Vasco da Gama, even Columbus) were directed at a specific passage, and merchants were also directed (the various Companies that were created by royal assent are a good example!), the Darien Scheme also fits (btw, this is funny that it does not appear in AGCEEP!).
If we want to make it a bit more random, some stupid idea would be that explorers/conquistadors, when sent to an unexplored province, would have instead some random chance of going the wrong way (in another unexplored province, or even turned back by a storm!). After all, even though they had some precise orders, the weather ruled supreme. I'd like it to be tied to the Manoeuver stat; Explorers could also be ordered to make landfall to discover a land province. This could also apply to settlers: they could get lost on their way, and mistakenly settle in the wrong province (wasn't the Mayflower Virginia-bound?). But I fear that this could become really aggravating.
I definitely agree with tying some possibilities with tech. The fact that the infra/trade techs don't have any «*goodies*» after level 4 or 6 has always been a big disappointment. As far as choosing the level goes, I would try and match this to history; so the «*force embargo*» diplomatic action should require about infra 8-10. Likewise, high trade level should enable some blockade-running to be done: for example, a blockaded province should maintain a portion of its trade value, and blockade should not be as efficient for sieges (or you would need a larger fleet). I think this was done in the American independence war, but not much before; correct me if I'm wrong. And since trade research represents the capabilities of merchant ships, this is certainly the good tech to tie blockade-running to.
And a couple extra ideas.
* The Manoeuver stat is a bit useless right now (except for attrition). It could be used for the first assault in a battle (thus being more important in rugged terrain, which seems fine since a plain like Waterloo doesn't help the good manoeuvering generals!). Some of the greatest victories of the time period were done by manoeuvre alone (Frederick II at Rossbach, Napoléon at Ulm). This could also be used to hide your real army strength (again, Frederick and Napoléon played this game a lot).
* As we all know, the number of troops in sieges is a bit wrong. Maybe a high fortress level shouldn't increase much the numbers needed to siege a province, while it could give a better advantage to the defending garrison in an assault, thus effectively requiring a bigger army to successfully assault it. (This is obviously linked to the above-mentioned blockade-running). The bonus to the garrison should be additive and not multiplicative, so that it accurately gets proportionally less interesting as technology improves (a medieval castle is useless against artillery, and Vauban fortifications were going out of style in Napoléon's time). This could even be more detailed: each time you make an assault, you have a chance of taking *some part* (bastion, half-moon, ...) of the fortifications. When you have taken enough, the city is yours. (Think of Orléans before Joan of Arc: the English have a well-started siege since they hold some of the towers). This would make sieges a bit more climactic, which is always good.
It makes so many problems which causes the MP community to not grow large. Too much hassle and in the end it doesn't work. 
