A thing I haven't seen much discussed but that seems important: fragmentation of the utxo set when there are 100x more users. Utreexo is one way of approaching this, but I'd be interested to be pointed to discussions on the topic
+1
Imagining high on-chain fees + utxo fragmentation into quasi-dust is scary.
For this reason I'd rather the value of Bitcoin go up relative to world currencies than the feerate increase by too wide a margin.
I'm also interested in projects like ZeroSync that make it easier to run a validating node. I feel like this aspect of Bitcoin doesn't get as much attention as it should