Let's face it - the lockpicking perk tree is not very interesting or compelling. There's basically nothing in the perk tree that demands critical investment. So here is the obvious, straightforward, so-simple-yet-so-right way to improve the lockpicking perk tree: the perks should make it just POSSIBLE to pick the lock - not easier.
A return to Fallout 3's lockpicking basically. For example - If it's an Adept lock, you need to have at least 50 in lockpicking and the "Unlock Adept locks" perk. If you try to unlock a door without having the appropriate perk, you get the message "you lack the skill to pick this lock" - just like in Fallout 3.
Think about it. It makes investing perks in lock picking actually significant and meaningful. It means new areas are available, access to unique treasure/environments/items/people etc behind locked doors, and so on. This was great in Fallout 3/New Vegas... you come upon a door with a Very Hard lock, and you are instantly curious about what wonderful item lays beyond - but you can't get to it yet... Giving you the incentive to improve your character to be able to unlock the mysterious door later.
This should return in Skyrim. Being denied access to areas unless you spend perks in Lock picking... would really make the perk tree feel actually worthwhile.
It seems like a valid change, but there are several factors different between Fallout and Skyrim that make this idea not work.
In Fallout, you assign skill increases at levelup, and in Skyrim you either have to train them, (horribly expensive after 50 skill), or increase them by practicing the actual skill. Since the perks have skill requirements, a change like this would pigeonhole everybody into training and perking locksmith or getting shafted out of treasure. So you would either have to pay trainers fortunes to get the skill - to get the perk, or you would have to grind grind grind on a source of easy locks to build the skill.
I have to say I don't see this working. I was sad to see the open-lock spell go.