Are we playing a fantasy game: YES, no one is suggesting that in reality Venice conquered all of Europe if thats the faction you fancy playing
Should the game try and be as historically accurate as can: YES, as long as it helps immersion in the medieval world and enhances game play. I love history and try and put more in my game than most, but as long as we remember that is at heart a war game, and anything we do works for the majority of people who play SS, a little history is a good thing.
One settlement type: Well personally I dont like castles in the game. Blatantly they existed, but the question is simple for me: can the Ai take a castle from a player? I have never seen it do so, where as I have had my ass kicked out from a city. If it is indeed impossible for the Ai to win in a castle seige (or at best very unlikely), whats the point of giving the player such a huge advantage? I know there is the reverse, that its harder for a player to take such, but we all still do. If I could make it so all players settlements on the battlemap were cities and Ai's castles I would. But as not, I say it is better to use cities.
Buildings: no one thinks that all spies really come from brothels and all assassins from Inns, but buildings reflect a concept for what is happening in a region. Personally I try and make each faction I play as different from each other as I can, so I think that spare building slots should help us produce a unique feel to the factions. Even if its as simple as giving England Wool Trade, and France Wineries, it helps promote a feeling of difference and then replayability to the game,
The only glaring omissions historically are atm imo
Monasteries
Jewish Communities
Slave markets - although I use these as mercenary barracks and so do not need a separate chain
and maybe the Arsenal in Venice
After that, it really is what you fancy to make each faction more fun. Personally though I like a colonization chain to reflect that you must change an area to your culture before you can produce your beloved units there and a Independent Peoples building to reflect factions existence and unrest at being conquered eg . Serbia, Armenia etc. This could also work for capitals as well so Paris is always unhappy if not french etc.
I would also love to sit down and think of a better way to handle relics, and maybe have a building for these. I think though it would have to be on the menu and be scripted as an achievement. Also I am not sure how to balance this for the Islamic factions.
Recruitment: As the Ai is not the brightest of chaps, I think joining the Barracks, Stables and Archery chains together makes sense, that way you dont have to rely on it producing the right type for its best units.
Interdependent Chains: Much as I love this idea - that you must build a stonemasons and a blacksmith before you can build a church for instance, I worry that the Ai can get it, essentially that is always our stumbling block in game
I would also like to figure a better way to deal with pilgrimages, atm you just get the trait if visiting the right zone, but idealling I want you at the right spot, so a map resource would be nice maybe, St Catherine's Monastery not being on the map atm is a tad annoying.
Costs: Well most buildings need a major overall in costs as they are way to cheap, but I would like to see 7.0 make churches more needed eg need a % religion to recruit, and at the same time have a negative effect on your income. All those requests for alms and need for land, and lets face it to much money spoils the game.