The thing that really frustrates me about Wallet is how much better it could be if Google would just get out of the way. The degree of gatekeeping they feel like they need to impose on who can integrate into Wallet just means that less services support wallet, so there is less reason for users to bother, so there is less reason for orgs to bother integrating in the first place.
I don’t get why they don’t just define an API (or better, an open standard, but this is Google we are talking about so I won’t hold my breath) that supports a few common patterns for prepaid transit cards and loyalty schemes - orgs just build an integration, register it with Google, job done.