I really don't think it will change that much, and this is what the majority of the community has been asking for with this item since they gave it more crit.
I have played both of these champions, I've played GP a lot on a smurf, and I play Yasuo in normals a lot with friends. It will change build paths, but in reality, the current Tri Force wasn't made for the champions you listed. It was actually changed so more ADC's would take the item. Since that isn't happening, it has to be changed. I also kind of doubt that Gangplank or yasuo will be hit that hard from this. GP can use CDR a lot, and there are plenty of other crit items out there. I also kind of disagree with Triforce, Essence Reaver, and IE being the only attractive Crit items for him. People believe that he doesn't auto attack in teamfights but to most effectively use his passive I attack with him all the time.
In all, people are overreacting to this. Most of the Yasuo's I see build Stattik-PD into damage items anyways, and most GP's are mid lane because top has turned into the tankfiesta, so he needs to be more glass cannon anways. I really don't think it will effect them as much as people believe it will. It helps the champions that originally synergized with Triforce anways, because most of them didn't need the crit in any way shape or form.