Fishing has made appearances in San Andreas (though only briefly) and RDR2 (where it played a significant role). Whether GTA 6 will have fishing remains to be seen - let's explore how it's featured in previous games first.
Fishing in past Rockstar games
GTA San Andreas featured fishing as part of a tiny minigame in some side missions. RDR2 took fishing very seriously with rod types, lure selection and fight mechanics. GTA V didn't even have fishing.
Whether GTA 6 sees a return to fishing is a design choice, not a technical limitation.
Why the Florida setting suggests it
Real Florida has a big fishing economy. Charter boats, pier fishing, deep-sea charters. Vice City's marinas already have the visual vocabulary of fishing. The bar is low for Rockstar to throw fishing in for atmosphere; medium to make it an actual system.
We won't commit to anything. We will say it's plausible.