Maybe it'd be easier to just make a special GTA: Switch? A different game. I'd rush out and buy that. Some new city?
I'd like to think we're past the era of "special game for Nintendo users". Usually we got the inferior product while the "real" game went to Sony and MS. Third party exclusives is 2001 style thinking and it took Nintendo way to long to learn that. In the present day third parties want to make one game for every platform so the Switch should be included in that. The exclusives that make a console unique are first party.
I would want Nintendo to be able to get whatever the other systems get for GTA (ie: the inevitable GTA VI). The portability of the Switch gives it an edge in multi-platform games since there are those that will put up with slightly weaker graphics or frame rate to be able to play the game on the go.
If storage space is an issue then perhaps Nintendo needs to figure out a solution for that. Maybe a later Switch revision needs more built-in space or as the years go by cartridge size increase as the tech gets cheaper.
Having played GTAV I can say that a lot of space issues have more to do with data inefficiency.
The thing about having an Exclusive designed for Switch port is they could probably make a better game. GTAV has been out for quite a while, so it lacks some newness, but getting GTA on a portable is imperative. I think this might be one of those cases where it would be more efficient to make a new game than to port it. You could make a port, but I see lots of issues with this just from a time perspective.
Though, they could also re-make the game more efficiently. It's complicated. I wonder how many redundant files are in GTAV. The game doesn't seem like it should be significantly larger than Black Flag in size. Also, from an experience of playing games, it's basically Shenmue times 8 on a better engine. If Sega made the same game it would probably be 30 GB. Nintendo already made a few bigger games with less space used.
One thing to look into would be putting GTAV on the back burner and making HD remakes of GTA3, GTA:Vice City, and GTA San Andreas. They look like garbage today and could use some polish. Also, A lot of people have Called for a better version of GTAIV. GTAIV only requires 18 GB of space.