Bitcoin nodes could also keep a spentness status list, where each bit in the spentness status list corresponds to whether a txo in the MMR is spent. This could make it so that disconnected wallets didn't have to guess the pruned relative spentness status when it reconnects to the network... and help prevent DoS attacks.

Keeping such a bit list would consume considerably less space if stxos were never added to the MMR. Putting portions of such a list in the node at height DLH_REQUIRED would made R/W operations on the bit list more local to other data that is going to be R/W.