It does not have to be realistic. It does not have to be a direct sequel (could also be a part 5 of a comletely new IP). Could also be a prequel. Could be different genres than the original. Could also be a different dev team, or a vastly different budget than the original had. Could be a sequel even though there is already one you just don't like very much. Could really be anything you want.
I'll start with an example:
Uncharted 4 released in 2016. That seems already long ago. But still longer if you think that a new Uncharted game will not be released in less than 1 year before its announcement. And we will not have such a thing a suspect this year. Meaning I could see the earliest next Uncharted be released in 2024. That is an 8 year gap and frankly already too long. There are so many possibilitys with this franchise. And it is somewhat in the discussion again, since the remaster bundle is coming soon. So a hefty sequel is in order:
Uncharted - Cutting loose
Cutter is going to be the protagonist. Nathan is completely out if the picture. Cutter is quite crazy and has no family responsabilities. He is rather shady and ready for a lot more dirty work than Nathan. But the tone is not gritty seriousness. It is lighthearted, funny (way more dark humor), gory (just a bit). Cutters perspective is unreliable. Sometimes he could forget what exactly he is after at the moment. He is violent and a bit unpredictable. He is a loose cannon doing things his own way. He is definitely not as good a treasure hunter or historian as Nathan is. And he will have to partner up along the adventure with somebody he does not like. Perhaps Sam. The treasure in question could be the Merchant Royal - 2019 they found hints to where it could be. It could take place in lots of parts of Britain but a bit of globe trotting is in order for a true Uncharted. Perhaps Russia, Australia, Eastern Europe, etc. Maybe the treasure is not that important after a while and it is more about them trying to keep their heads above water as the people they have to deal with get ever more dangerous. But it should still be a silly action blockbuster - perhaps a bit like KingsMan, just not spy stuff (or not much of it) and more focused on the action / adventure of it.
How would your dream sequels look like? Would you drastically change the ip? Would you unearth a long dormant franchise (legend of dragoon)? Would you set things right for a sequel the devs botched? Anything is on the table.