(And I MEAN just Octo Valley. I think remaking the entire first game would be kind of a waste of resources and might possibly mess the timeline up in some way...)
Personally I really think they should. It's just kind of awkward having it be the only campaign not playable on the Switch/Switch 2, particularly since that means a lot of fans are unable to experience the entire story (myself included actually).
It would also be nice to see what additions and improvements would be make, particularly in terms of the lore as the world of Splatoon was pretty self-contained in the first game and so they could expand on certain things now that they have a much clearer vision (for instance, why the octarians specificially had to go underground when they lost and not just elsewher on the surface).