My thought with the poor modifier was that it was an intrinsic characteristic of the province. An empty patch of desert will always be an empty patch of desert, no matter what you do. Building irrigation (trade good permitting) intrinsically counteracts the poor modifier, but it shouldn't remove it and put Oasis Parva on par with an Arid province in Persia, for example. You have to figure that irrigation/forums or other buildings will always be built eventually, it's just a matter of when the money becomes available. As such I'd be reluctant to have a mechanism for removing "poor" from even the non-desert provinces. My understanding is that places like Corsica were never particularly valuable in this era. I could see an event removing "poor" based on population, particularly if growth rates were better constrained. If you can get one of these provinces to 20 pops (or whatever), congratulations, it's not "poor" anymore! 
Regarding a Trin Tragula style population growth system, it will require a lot of care, unfortunately. The value that seems approximately right to tie to the civilization value (0.0005, +5% pop growth for a 100% civ province) is too small for the game to include it, so one would have to use larger values and then balance other factors to subtract appropriate values. I've seen civ fluctuate to shockingly low values (a few percent) for some reason, so there could easily be pathological situations which would quickly deplete the province population. I also couldn't get a revolt risk modifier to work. Setting city_population to -0.001 (-1% pop growth per 10 pops) worked, at least.
I like the uber-grain and olive trade goods, and will be interested to see what the other two do. Ivory seems redundant with elephants, unless you're extending the map far to the north. Or was it only the Greenland Norse who had walruses to hunt for ivory? That would be a CK mod anyway...
Will the migration event gain an option to decline? I don't think it's possible to get uber-grain to Seleucia, so there would eventually be perpetual grain riots there. A historically strong late-period Parthia could run into the same problem. EU3's "move capital" ability would also offer a way around this, but I doubt that can be modded in.
Regarding a Trin Tragula style population growth system, it will require a lot of care, unfortunately. The value that seems approximately right to tie to the civilization value (0.0005, +5% pop growth for a 100% civ province) is too small for the game to include it, so one would have to use larger values and then balance other factors to subtract appropriate values. I've seen civ fluctuate to shockingly low values (a few percent) for some reason, so there could easily be pathological situations which would quickly deplete the province population. I also couldn't get a revolt risk modifier to work. Setting city_population to -0.001 (-1% pop growth per 10 pops) worked, at least.
I like the uber-grain and olive trade goods, and will be interested to see what the other two do. Ivory seems redundant with elephants, unless you're extending the map far to the north. Or was it only the Greenland Norse who had walruses to hunt for ivory? That would be a CK mod anyway...
Will the migration event gain an option to decline? I don't think it's possible to get uber-grain to Seleucia, so there would eventually be perpetual grain riots there. A historically strong late-period Parthia could run into the same problem. EU3's "move capital" ability would also offer a way around this, but I doubt that can be modded in.
