I think having a Pope Emeritus is weird enough for people in the Vatican--having two is a different story. Add that to the fact that contrary to the Pope movie, I'm pretty sure Francis and Benedict dislike each other and may not want to spend their last years sharing Papal spaces or splitting whatever homes the Pope's estate would give to them.
The Two Popes was obviously a work of fiction, but Francis & Benedict already live in adjacent proximity to each other & are said to be on legitimately good & friendly terms with one another, so I don't see that being a part of the consideration. (The weirdness of having 3 living Popes at once, on the other hand...)
Is this part actually true, though? Cause the things I've read imply otherwise. Though it's possible that Benedict's people and Francis's people are the ones that genuinely despise one another, and not the two Popes themselves