You've hit on why cross-disciplinary collaboration is difficult to foster (people either need to be pretty good at communicating with folks outside of their discipline, or they need to have an interest or discipline in common, but the people involved ideally need to have deep expertise that is not shared. So often you see pairs where each one's shared interest is the other's deep expertise, which happens a lot with pairs of fields that complement each other in an obvious way (eg. 3D imaging and archeology).

Generalists shine when they bridge people who don't have much in common with each other. There are probably ideal ratios of "glue" people to have within a collaboration and within the groups from which collaborations arise, but I don't know what they may be, except at the low end (2-8 specialists need to have at least one generalist if there is nothing else bridging the gaps).

Keep in mind that there are generalists and then there are generalists. Some people tend to have a wide array of interests and seemingly manage to be the second best at every one they pick up. Collaborations tend to form around them spontaneously and they are a specific subtype of the 10x practitioner. We can ignore their existence for purposes of this discussion.

So, back to your question. Generalists connecting and working with other generalists fail the "deep expertise" requirement, which may not be a problem if there is a lot of low-hanging fruit to be found, but otherwise a concentration of generalists isn't particularly fruitful (except for social or recreational purposes, but we all like our groups to do double duty these days).

You would think that a large group of generalists would at least be great for generalists to introduce other generalists into groups that would fit them, but it turns out that having a very small number of hyper-connected individuals (who don't even need to be generalists themselves, really) salted though the social graph serves that purpose more efficiently, as well as introducing people who don't need a bridge builder.

My advice is that rather than trying to find or create a large group of generalists, you join a group that has a diverse, even eclectic set of people in it. Some interests tend to collect weirdos from all walks of life that tolerate each other's obsessions that they don't share, and you'll find that you always have something to talk about with everyone (even if it isn't the topic that the group is ostensibly organized around), and you'll also find more than the usual number of generalists or semi-generalists among them who were attracted to the group just like you were.