I think I want to answer this question by first acknowledging how the community must feel about joint account features in general. I worry sometimes that it looks a little like folks’ very fair and reasonable requests to bring Plus/Premium parity to joint accounts is falling on deaf ears. We often say something like “we’ve been thinking about this!” Or “thanks for the suggestion!” and then you hear nothing more about it.
And then someone asks again, and the same things happen. But I think it’s really important to note that a lot of folks at Monzo really, really, really care about this problem and we do think about it a lot. The honest truth is that we just haven’t got round to it yet. We know there’s hundreds of things we could do to make joint accounts better (including making them compatible with Plus/Premium features!), but we’ve been busy working on Trends, Flex, the improvements we’ve brought to Flex and virtual cards on Pots and some other things too 
I can’t say when we’ll properly tackle this problem – because I don’t know! But please do know it’s on our minds!