Generalized req is something I was asking about, about a year ago now. And I somehow got the impression that they were comming in 2.6 now I hear that that is not happening. Which is very sad.
In addition to that, I belive reqs "vectoring" could use an extension overal. Currently it is only possible to specify requirements like so: "[some stuff AND'ed] NOT [some stuff OR'ed]", and you can't have some effect/building allowed by one or the other thing. Suppose you could have unit that is available if you have building in a city, OR some wonder in any of your cities (OR maybe some tech).
Alternatively, most awesome option would be to have something like can_build(city, thing) lua function, that could process all kinds of stuff (though doign some things in lua is crazy complicated currently, for example checking if/what wonders player has) and would allow tons of flexibility. Though obviously this makes AI stuff cracy complicated, possibly some "AI hinting" lua functions could help, still everything would be very complext with regards to AI. On the other hand, maybe it would be possible to simply allow mark ruleset as multiplayer only/no AI and don't sweat so much about it? I think such marking is basically possible, set AI fill 0 in ruleset and dissalow changing of that option, this should make it alsmos AI'less ruleset
though server admin could probably toggle that using server console at run time, still...