Some really great thoughts!
Just a few notes:
Curve does that, and it’s so annoying! In Curve you often have no idea how a transaction amount came about, as the original transaction and any refunds are just folded into the same transaction. Just my opinion, of course, but I hate it with a passion 
They are planning to do that, but it turned out to be more complex than first thought, so it might still take a little while. But it’s already being worked on, I believe.
Monzo have said somewhere (I think in connection with the coin jar / feed tidy up project) that one of their main aims is that the feed items need to add up to the total displayed. For that reason I assume this won’t be happening (and indeed, being a pedant, I’d hate that - see my first comment on removing £0 items 
)
You can at the moment do this manually from the bottom of summary tab, or from the account > settings screen if you need data for the past months.
If you wanted to automate it, you could probably do so using the API, if you know how to do that sort of stuff and have a spare half hour.
I wish I could write that clearly and use formatting on my phone 