Would absolutely like not precisely skill trees, but talent trees, with 2 conditions:

1) they must be done so that each job always remains the same role. For example, for PLD there can be a choice in his tree between two talents:
A - "increases Sentinel duration by 5 seconds", and
B - "all healing recieved during Divine Veil is 10% stronger"
Both are corresponding to the idea of tanking. Vice versa, "increases Clemency potency by 100" would be a bad talent.

2) they must be balanced so that there is no meta implicitly forced by devs. Blizzard is infamous for doing that on purpose - no thanks. All builds must be equally good at least on mathematical level.

Apart from that, I see no cons and 1000's of pros to the idea. You would be able to make your job and your vision of it unique. Ain't that cool.
Of course, it implies a huge amount of work and sadly we won't see it most probably.