I really, really doubt that will happen. As in under a 3% chance.
Adding additional skill sets is a lot of work: animations, artwork, design, balancing... During the early Kickstarter days I suggested adding a 3rd vote for more skill trees as a stretch goal, but they were more interested in... other things.
If they were going to add in more skill sets, they would just have said "Polymorpher is going to be in no matter what, so pick two more."
I agree....especially since Polymorph, Summoning Master, and the Shapeshifting Mask aren't even in the game yet....I honestly am worried that even these three things may be in trouble, forget extra skill trees.
