Any second layer solutions for bonds would have central points to fail?

For a 2 layer solution, you could setup a N-of-M multisig that works in a similar way to decentralization via witnesses at the 1st layer.

This ui for creating accounts and allowing deposits to the wallet seems trivial to me, yet nobody has done it. Am I missing something?

I'm not sure of exactly what you're asking for. Do you just want an account creation feature inside an open-source UI, as opposed to the current closed-source ones?