Can we pay this $1 with Bitcoin or only with fiat currencies?
Apple and Google do not allow this for mobile apps. They also don't allow cheating (i.e. charging off the app and then using some kind of coupons). But if they will eventually add a feature to pay for in-app purchase by crypto, then you will be able to.
This won't be an issue when Crosspass is released as a desktop app, and in this case it would accept directly a crypto payment.
If I had to receive Bitcoin address from someone and this guy told me that first I have to install new app on my phone, I would immediately think that this guy is a scammer.
I have seen way to many real life cases of people getting scammed like this with fake apps, so I would probably refuse to install anything.
This happens rarely in iOS and with time Play store will up its game.
There is a chance I would use something like this if Crosspass was integrated in some messenger used for private conversation.
Yes, I am also exploring this direction. But the standalone app will continue to exist in any case.