1. This seems to only work between Proton accounts, so I doubt many would actually do that. And it seems they’re using the regular BTC network, not Lightning, so fees are going to be huge ($1.60 from their screenshots). Monero solves this way better since there’s no way to see someone else’s balance with their address, and transactions are pretty cheap (a few cents). Their solution doesn’t actually add privacy, it just obfuscates transactions a bit. Lightning does a much better job w/ privacy (it’s private until you close the channel) and costs (transactions are way cheaper and way faster than regular BTC), and it would be the ideal solution to this problem since it still uses BTC.
2. Sure, but aunty is highly unlikely to be using Proton, much less Bitcoin. It’s a service for enthusiasts. Support is absolutely important though, I just don’t think aunty is likely to be sending crypto over Proton.

I still don’t really see who this is for. The requirements to actually using it productively is that your contacts need to also have Proton. If most of your contacts use Proton, that means you’re probably running a business or something and thus don’t need to send BTC to eachother.

Focusing on regular users makes way more sense than focusing on these niche use-cases. Make it so I can easily use cryptocurrencies for online payments. Integration with Proton Pass makes way more sense than integrating with email.