I think there are plenty of people living in communal housing on some level or another. In my city I've met several who have shared larger townhouses with several bedrooms and shared living space (the simplest would just be looked at as having several roommates I guess) or large warehouse/loft spaces with similar arrangements.
I don't know of any full apartment buildings like this though. I guess the main issue is the one that comes up often enough with the smaller groups I've run across: stability. The more people you have, the quicker the odds of "turnover" go up with people moving in and out. Adding to this is the sense of ownership or control that tends to keep people living in any given place. If you feel like it's really your home, then you want to stick around but the more people split "ownership" of common resources, the less each individual feels it's their home.
I think on some level everyone wants to make their home the way they prefer and I guess the apartment building idea would be good for this. You have enough individual space to fulfill the desire to have your own setup but you share the parts that make sense to share.
I guess my question is where the line is between just good neighbors on a block who share some activities/resources and housemates in a big building when defining a potential community or collective.
I think there are so many degrees of community that there's not really a set point at which it becomes a collective endeavor. If you go by just living in the same structural building, then there are certainly plenty of examples right now. All you really need is a building where residents all have some level of agreement on things to be shared and contributed to.
The flip side is that the only real way to ensure it happens is to buy the actual building and only rent apartments/sell condos to people who agree to the arrangement. If you don't have a replacement for someone who is moving, can you afford the vacancy while you look for one? If residents own their own condo/unit, can you compel them to only sell to someone who would follow the "house rules"?
I can see why these things tend to be more along the lines of lucky accidents (neighbors who all choose to contribute to some degree) than more formalized arrangements.
One simple, ideal way for my utopia to really happen would be to have a wealthy patron who would be a benevolent dictator who own's the land and the building, and has ultimate responsibility for keeping the lights on, etc. The benefit to him would be the same benefit as to us all: to live simply, peacefully, among people who are striving for some level of moral perfection. Key to this would be a) sharing values, and b) having a minimum level of success with those values that your presence would not be disruptive.
Yoga and meditation tacitly imply the kinds of values I mean: morality, concentration, wisdom (actually, the 3 parts of the Noble Path of Buddhism). Part b comes from my experience: I have met many people (myself included) who believe in the path but find it difficult to stay on it. I suspect that it is far, far easier to walk the path among others with the same stated goal, and that would be the main thrust of such an experiment.
A benevolent dictator would solve the problems inherent in determining who should stay, who should go, and why. I'm less concerned about malicious people than about well-meaning people who are, through no fault of their own, disruptive because they cannot control their own behavior. Any group can survive a certain amount of this; but how much? When is the threshold reached?
Of course, benevolent dictators are hard to find - and of course, people change, so a BDFL my slowly morph into something different. One possibility is to make the BDFL a computer program, one that is revised according to certain stringent rules involving consensus. The ideal program would be extremely passive, pushing gently here and there, sometimes in quite unexpected ways, to correct patterns that it predicts will yield a terrible outcome if left unchecked. I think such a thing is possible, but may be outside of the realm of possibility as of yet, since it requires such complete modeling of personality.
Seriously what prevents likeminded people from doing exactly the same today?