Will the user be forced to have a noncustodial wallet?
Discussion
Or is the automatic withdrawal optional?
yes
Seems like a decent tradeoff.
The only thing I would suggest is the ability of users to open an external wallet on zap IF they go full retard like me later on. Like how Amethyst will open Zeus when I zap someone. But I'm not an Apple user, so my UX preferences may not work or make sense in that environment.