There is a quest involving Sisipu and some monstrous something or other at Brewer's Beacon being added. That's all there is related to "big fishing" in the patch notes so far. Most likely what is going to be the case is that this quest will have you fish up some key item type fish that you bring back to Sisipu, and as a reward you get the fishing bench offhand tool. The tool will naturally give a huge boost to the fisher's stats, and that might be all there is to "big fishing" - ie, nothing at all except making it easier to catch the biggest fish by giving fishers a stat boost. Which isn't needed since a fully geared and overmelded fisher can already catch hq versions of the largest fish in the game without fail anyways. I really hope I'm wrong on this, but there's my take on it....