religion: it was an important parameter in the game. but it is not a core issue of the game. corporations are like religions as well, not a core point.
the most core issue of the game is food+hammer(shild)+commerce system. i will be glad if that doesn't change. if it changes, then it will be a real different game.
i wouldn't like the mechanism howa city pops to 4 from3.
i wonder about such things especially. is production similar? how is science researched? AFAIK, great people still exist, so i hope commerce and tax slide is simlar as well. i hope they wouldn't change such core points of the game.
also the happiness/health cap system of civ4, and espionage points mechanism were also fine.
else than these, the rest is not important much. w/o religion, game will still be fine.
i even can have a taste playing civ3, so why not play w/o religion?
civics: a change in this might be fine. still, i used to like the civics of civ4
traits/unique leader: traits were fine. there were great synergies. and each leader could be powerful if it was played cleverly. but now each leader will be unique. oh, i start to feel that the extras would be simple. i hope, it won't be.
for example, to get benefit from gandhi you found religion and assign priests specialists, right? at least you do sth. this is the favorite play style of gandhi and you know this, you apply.
if gandhi had such an advantage than other leaders: growth +5%. so each pop would come as 95% of required stock. it would pop up in 48 instead of 50. so this would be too simple.
or how would u play lizzy? you would make some cottages and assign some scientists and build academies in cottage cities, right? if lizzy had this feature: gold +5%. would that give u fun?
shortly, i expect good extras from leaders. extras should be useful only when it's played cleverly. i don't want no-brainer extras of leaders.
finite resources: that would increase the need for wars. could be great if implemented well.
better AI: i expect much from this. one person said that "i don't want AI to start with one extra settler", i agree with this. i expect AI extras to be better when we move up level. this is just similar to a football match between father and son and son starts with 2-0 ahead
city states: don't know what to say yet. what about barbs???