I really enjoy fishing in the game, finding the different fish and reading on their lore so I'd love to make fishing even better in this game. Here are my ideas down below:
1) Crafting items/armour from certain rare fish such as the Serpent of the Deep.
2) Findable/Buyable bait that'd increase the chance to find rare fish
3) A set that'd improve everything to do with fishing. Better selling prices for fish, longer hook times (means you wouldn't have to react quite as quickly) and more in return for being useless in combat.