So in almost any MMO i've played the fishing has always been really boring. FFXIV had some decent fishing but it got really boring really quick and all it was, was something to do kinda like a pokemon version of fishing where you're basically checking off boxes of fish you caught. The mooche system was okay but it was just dealing with RNG mostly. You catch a certain fish and recast it as bait to try and catch a bigger fish and that's it.
Ashes want's to use what has worked in other MMOs like how SWG will probably influence the Animal Husbandry profession but there's nothing I would copy from another MMO for fishing.
My idea would be to go back in time to the NES/SNES days when there were lot's of fishing games on the market. I think these old games can be used as an influence to create a better, more engaging fishing mini game that you don't see in MMOs
Here's a short video review (less than 4 minutes) of Bassin's Black Bass With Hank Parker by SNES Drunk, This one game I think would be the perfect game to influence the fishing in Ashes
https://www.youtube.com/watch?v=FWX_wTUZ8S4
devs would probably need to fire up an emulator and play this game though to get the idea of what to use in the game though.