I think you’ve pointed out some really key use cases here, which will definitely need to be addressed as more functionality & integrations are added to the app.
Given the fact that there’s limited space in the transaction feed though, especially for some users, there might be other ways to make the items that you’ve mentioned easily accessible…
It looks like the new cards / accounts design would be the perfect place to store a loyalty card (& account data) -
Screenshot from this post.
This is going to be key…I agree that attaching the bill splitting info to a transaction without a way to see a consolidated list of pending payments might not be enough.
Those are now easy to access in the Contacts tab 
Search might be the solution for this or something else…