I'm not sure that Grappling as a skill would work thematically unless you also use weapon groups (from UA) as a skill. (Granted, I re-determined the weapon groups for my campaigns.)
If you went this route, however, you would - I think - need to either grant a Defense bonus to the classes or - more likely - change AC into a skill as well. Perhaps there could be two defense skills - Dodge (dex) and Parry (str). However, altering AC in this manner would make applying bonuses to it odd - unless you also changed armor to DR - in which case the PCs and their foes would get hit more often, but would take less damage.
Finally, to prevent any type of overpowering, you would likely need to implement - at least for combat skills - a maximum of one rank over current level. If nothing else, this would allow low combat characters to maximize defense and perhaps one other weapon (rays? light blades? bows?) and high combat characters to maximize one or both styles of defense and several weapon groups.
All this, however, would change the flavor of combat quite a bit, and its balance is arguable until it is play-tested.