The 10M size is a combination of back of the napkin calculation and also my intuition. I think ETFs and other layer 2 solutions will help keep fees manageable for UTXOs of that size and perhaps 1M too.

And for the # of UTXOs that’s my opinion. I’ve had to migrate/change multisig set ups and manually sending each UTXO is a pain in the ass if you have a lot. I think having ~20 UTXOs is manageable from that pov and also lets you spread your wealth enough so you’re not doxxing much of your holdings when you’re making any one txn