We’ve now got Sustainably, Flux & Tail running live closed betas (I know because I’m in all of them 
) so it looks like Monzo are giving permission to select 3rd parties to integrate with their API.
I’m quite thankful for that, given the delay that there will before the API is officially ready. It seems like it’d be a waste of time to wait until then to start testing.
Especially because there’s people trying to build businesses on the back of these integrations - both Sustainably & Flux have integrated with Monzo 1st. Or to look at that the other way, it seems very risky to start with your businesses 1st integration as Monzo if it’s unauthorised..
Edit
Also, as far as I know, the only limits on use of the API have been technical, rather than legal.