So I seen some different pure builds, but not too many. I think if we made it so we could lock our combat xp, say 50m per skill, but still allow us to see the xp drop from the hit. So say if I lock my attack xp as a 75 attack 1 def pure, and i ags spec, but herpy derpy switched so to attack xp and hit a number. Not so bad, but over time I could level up without noticing.
As of right now if you lock your combat xp, you don't receive xp drops. This isn't too big of a deal imo (could be wrong) that could motivate some people to try pking out, and would be a better gold sink up front as the 1.5m gold to reset ain't much and I've only had to do it once in my pking adventures as a pure.
Edit: And if you want to unlock the xp lock, it could cost 10m. I'm iffish on this tho cuz it might discourage people from locking if they are not sure about the investment.