I think the key question here is - will the next game be 9th gen, will we get another game along side sword and shield, or will we get another expansion?
I think we should get another expansion - this gen almost feels like I'm playing an MMORPG, so by having another expansion, we still can freely travel to the old locations and use those resources, without switching game etc. Keeping all your Pokemon in the same boxes and stuff will be helpful, too!
Just makes a lot of sense right now, tbh.