Yeah for one I like the idea that you're separating your spending from your routing. That's a great idea, and you can even take the initiative to set up your routing node to either not use any of your own UTXO's at all (by buying/leasing channels) or you set it up with a few coinjoined UTXO's (just keep in mind there's some consolidation happening there).

As far as the spending node, I think that would have been a good solution because of the "not possible to reveal the UTXO of a private channel hidden behind a public one" case. Great job on that! Though the good news now is that I believe all major Lightning implementaitons support SCID Alias so you can open up a single unannounced channel with that flagged turned on (the other channel partner also needs to support it) and then now it's not able to be probed. In both cases though, your channel partner will be aware of the UTXO, but not anyone else which is a great improvement.

I really like the idea of spinning up a new node for each UTXO and spending down that balance completely. Though it's hard to do in practice which is why I'm prioritizing that in Mutiny.