Can’t see it being other country accounts. Tom said in the recent Q and A that Monzos would need to acquire more banking licenses to do so. Which is time consuming and not on the immediate horizon
I don’t think it has to be a social network to succeed, but growth is necessary for them to become sustainable and go up against very well resourced banks like Barclays. Monzo are clearly on the radar of big banks now as they have copied almost all their features (card freeze, locations, gambling block).
Re growth there are lots of interesting features that can be built for groups like shared pots, bill splitting etc, all of which work better if friends use the bank too, so there are other ways of encouraging it. They certainly shouldn’t chase growth at the cost of user experience or pester users with notifications (agree with your other thread on that), but scale is necessary if you want Monzo to thrive.