I really like this idea: bundle addresses together and also automatically shield funds.
Bundling addresses together reminds me a lot of Signal. When I initially used Signal, most of my contacts used SMS (no encryption). But the primary reason I jumped on Signal was that it would work with any SMS contact but then automatically upgrade a conversation to full encryption if the other person also had Signal, so I didn’t have to switch between “the secure app” and “the normal app” to talk to different friends.
The drawback of that approach is that sometimes it’s hard to tell or predict (or explain to non-techies) how to tell when the connection is private. If the Zcash wallet ecosystem goes in this direction, we’d need a good UX norm of making the risks clear before the sender hits “send”.
OTOH, Signal now has millions of users. Another notable detail is that it had a built-in “invite your friend to signal” button.
So one vision is for shielded wallets to do the same. One problem is that there’s no (Zcash protocol) way to send your t-addr friend a message, so we need to think more about how to implement the “invite your friend to use shielded”.