I suppose they could do that. But it’d been Nationwide becoming an atypical case that would need Monzo to manage it differently to banks that do it properly.
The problem seems to be with Nationwide so I’d rather push the pain to them to resolve, personally, rather than expect Monzo to put a plaster over it.
I don’t quite know what you mean by “as normal” here. Monzo card payments are never presented in the app as pending and (frustratingly) categories for pending (greyed out next day) direct debits / BACS payments etc can’t be changed.
That said, I like the aspiration and would love to see it. Looks like Monzo doesn’t get quite enough data to do it properly though: