Couple simultaneous games sounds like an option.
As for goals I imagine them to be entirely different when ruler changes, as rulers, well they had their quirks and their ambitions, which did not necessarily align that much with the past.
About the "simple" rule based approach, I think it ether would not be simple (so kinda pointless), or it wouldn't be all that fun, likely nether. If we take such simple things as pop/trade cities increase, certain phases of the game would be much
more favorable to such rules, and thus people who get to play at those stage would be strongly advantaged (in regards to number of points they can gain) when compared to people playing at other stages. I think more dynamic voting based approach should lead to much more interesting games (baring sabotaging by players/voters), for example if you get nation on significant downward spiral it might be considerable achievement just to make things rights, but if your only choice to gain points is to conquer more land, you might see such situation as desperate/pointless and become quite disinterested, likely leading to even faster downfall of a nation. While with sensible voting, people attacking nation A, could vote like avoiding loosing more territory/establishing peace as a worthy goal for future leader.
I think some voting with some, possibly programmed, heuristics could do the job quite nicely, while rules could lead to some perverse initiatives, on the other hand, that does not necessarily mean that game wouldn't be fun. Also not that voting based stuff would be void of such things
If you get points for research, you might disband most of units just to rush library/uni building
. For such cases there possibly could be some penalties if during persons reign, certain parameters fall some percentage from the time they started.