That sounds good, based on what we’ve heard from Monzo so far, my guess is you’ll be able to replicate that functionality using a combination of joint accounts & virtual savings pots.
I’m imagining each cardholder having their own card & then being able to pool their money into a shared virtual pot. In which case, rather than having salaries deposited into a single account, the salaries would be deposited into each user’s accounts before being pooled.
Having said that, Monzo haven’t ruled out enabling two cards to be linked to one account. And my ‘design’ might make keeping track of the joint account holder’s transactions tricky.
It would give users greater independence though, as if you wanted to end the joint relationship (not you of course 
maybe flatmates instead), direct debits etc. would still be linked to an individual user’s account.
I guess it’s just a question of which structure is the easiest for users to manage. Would my suggestion work for you or potentially cause issues?