Or the four of them have their own teams and play off against each other. Winners goes on
Since Irish Rugby is unified four ain't the go: while I'm sure the possibility of an individual (or very small group of) Northern Irish person representing Team GB exists, the likelihood of total side worth considering at this level is v v small.
As said, I think the SRU & WRU would be happy to tacitly concede the GB place to England rather than overcomplicate issues. In the big tournaments (as said, this would be European/Repechage Olympic Qualifying and the games themselves, maybe the Sevens World Cup if that ever becomes a thing again and GB were obligated to play) there would be room made for XVs players that their Union is able to make time for. Japan is a poor example because of the pandemic, but both Bennett and Cross were dropped in for the Silver Medaling Rio team.
I would prefer to see a Scottish Sevens team funded and achieving top 8 finishes in the series as well, but the Olympic alignment is a political force rendering that supremely unlikely.