I hate the notion of having to comback to the dungeon that I just cleared simply to open a master level lock. Also how will this work in quest only areas you may not revisit? It works when you manually level up, because it punishes you for not investing any skill points in Lockpick, but if you have to reach a skill of 100 to get open master Level Locks, it would not work. The system you are suggesting will only work with linear chest difficulties, and this is rather lame, because it really doesn't add any value to the difficulty of the game.
Yeah, it doesn't work well with the whole "Open World" part of the game. But I seriously think that thieves should get more of a kick out of actually being one. It's stated that a character with the base 15 points in lockpick can open a master level lock. This in its own is ridiculous. What they can do is make some of the locks difficuly level with the character.This means that higher level characters will see master level locks more often and then only true thieves with applicable skills would be able to open them. I guess characters that don't invest in lockpick would be against this, but at this point investing in lockpick gives you no extra advantage whatsoever. That should be fixed.
And the fact that you don't want to go back to open a master level lock because your character wasn't good enough at it is not a viable argument. You can evade it by level scalling the master locks, but I don't even think it's necessary. You don't have the lockpicking skill? You can't open it. And that's how it's supposed to be!