Most people are pretty aware of how the mechanics of the electors work in EU3. You can inherit them to become an elector yourself, you can vassalize or PU them to get them to vote for you almost all the time, and making them like you will get them to vote for you, even if you aren't actually anything approaching a good choice, among other things.
What I want to see in EU4 is being an elector having a use other than making it easier to become Emperor yourself. The electors held a lot of power over the emperor, and could threaten him into giving them concessions or they would elect someone other than his designated heir. As it is the AI being an elector doesn't really help them, it only makes them into a bigger target. I would like to see at lest a limited ability for diplomatic options based on elector status, as well as some kind of way to limit people (and technically AI even though they probably still won't be smart enough to do this) from exerting massive power over the electors, like vassalizing them.
Compare how the electors fared over the course of history with other princes of the HRE. Saxony and Brandenberg both grew powerful, while others in the area fell under the Dominion of the Swedish and Austrians. The Eastern Bishoprics had less territorial expansion, but survived for a very long time. Maybe even a mini-emporor bonus for the military and prestige would help them out.
I just think they aren't given their historic power in EU3, and would like to see that changed in EU4. They obviously weren't super powerful first-rate powers just because of their elector status, but it allowed them to exert more influence than other states their size would have been able to.