Regarding bloat: This is not a difficult issue. First, there is only potential bloat once propagation delays are significantly higher than block creation rates, but more importantly,
The contents of off-chain blocks can be discarded after a short while (e.g., after 1 day). Only the header is needed to verify the difficulty was met. If a switch is needed to some previously discarded subtree, then the node that triggers it, can supply the contents of the blocks as well.