The underlying problem here is the lemmy community being spread out across many instances, and this solution doesn't really fix the underlying problem.
This is just speculation, but I think eventually 1-4 instances will grow much bigger than the rest. I think when this happens, communities will become much less fragmented and the problem will solve itself.
tl;dr while this is a good idea, I think if we just leave everything the way it is the problem will solve itself.