They are already making changes to AE. what else do you want? beeing able to make separate peace deals because it's historical?
then i want that the coalition will be able to reduce you to your starting size (maybe 100 years ago of the coalition forming) if coalition wins. That was also historical (peacetreaty of Napoleon).
That Allies/vassels can switch to the coalition side (bavaria and rhine states vs Napoleon)
That surpressed nations can rise and start fighting with the coaliton (prussia vs napoleon)
that you/AI can join coalition wars regardless when they started (austria vs napoleon)
higher Revoltrisk, reduced recruiting(lower manpower?) and worse soldiers(decreasing armytradition?) (again napoleon)
I would be fine with these, as by the time I get coalitions, I am already an unstoppable blob. I have yet to lose a coalition war. My one today was me (Austria), versus all of the HRE, all of Italy, France, all of Scandinavia, and the Ottomans, in 3 separate wars. I captured part of Greece (releasing Byzantium), I released a bunch of HRE members giving me points, and I got another province for my French vassal.
During this coalition war, my ruler died and put me into a regency. This regency cause most of my territory to revolt. Despite losing 20+ ducats a month having no manpower, I still won. I could have even done better if allowing for separate peace. As I could have negated almost the entire HRE in one go instead of 3.
You also forgot a few things in your list:
1) Napoleon and his wars weren't the only coalitions that existed, in fact most coalitions of this period had nothing to do with how the Napoleonic wars went. Most were over trade and religion.
2) Napoleon subjugated part of the HRE he was originally fighting (your southern Germany states example makes no sense as they started the war against France, ended up fighting with France when they initially lost, then the ones that were freed ended up fighting France again), using their troops to fight everyone else. In fact, the troops with the highest losses were those of the HRE members, as they were often used for cannon fodder. So suppressed/subjugated nations works both ways, fighting for and against the coalition.
3) When Napoleon came back after having almost none of his army return from Russia, he went and raised another army to wreak havoc again. Manpower in real life was not as finite and slow regaining as it is represented in the game. The equivalent would be losing your army, then getting a +manpower event span with a massive decrease in recruitment time.
4) Once you become the size of half of Europe, you often fight a few coalition wars at once (there seems to be a limit on how many countries in one war). In essence they can join a coalition war midway through (within how the game mechanics are represented). On top of that, if a new member joins the coalition, they can redraw in all the members that ended up being removed when part of the coalition peaked out, essentially putting you into a near never ending coalition war.