But user have to be technically minded enough, and willing, to set up a crypto wallet to do this.
True. That would be true of any platform which allows tips, you'd have to connect to some source of money whether it be paypal or crypto. Paypal's fees would be prohibitively expensive but it would be theoretically doable. Either way, it's a <5 minute setup process if they care to do it.
Interesting I didn't know AP supported E2E. I guess it's Mastodon that doesn't support that element of the AP protocol then?