I really disagree that the expectation is that communities will consolidate.

I think many users including OP overstate the problems of “split communities” and understate the advantages of having similar communities on different instances.

Having a /c/opensource on both lemmy.world and lemmy.ml doesn’t meaningfully “split” the opensource community. Users can subscribe to all, some, or none as they wish. So what if you see the same post twice - it’d not ideal but not really a detractor. It’s not the same as say, forking an opensource project or having discussions on both IRC and matrix.