(Hi, Lyn, long time fan!)

I'd push back on this, a little. There are definitely cases where I won't have a UTXO, but all the cryptographic solutions I've seen to handle others' failure (malice or incompetence) devolve to me obtaining a UTXO. 

In times (and places) of high trust people may forgo this security, but if you can afford it, why would you? "Verify, don't trust" is our entire motto at Blockstream, and while I am not my employer, it resonates.

In my mind, forgoing cryptographic protection for your Bitcoin, if enough people do it, is akin to detaching your issued currency from gold. Seemingly a minor technical detail which has no immediate effect, perhaps. Obviously nobody would be foolish enough to do that, though! 😬