I just wanted to run this idea with people to see what they thought. The idea was to remove level requirements for perk upgrades and replace them with additional SPECIAL requirements. The interesting part of this is that the requirements would not always need to be within the original SPECIAL category.
For example Sneak requires 3 Agility to unlock and has 5 ranks. what if the higher ranks required points in perception instead of a level to unlock? You could even increase the required level of both Agility and perception for higher levels of sneak.
Some perks could simply require higher levels of the same SPECIAL, like Toughness just requiring more Endurance.
If done right I think it could make an interesting alternative to the existing system. I'm guessing it would make it a little harder to max one or two SPECIALs and ignore the rest. This would also open up the ability for players to access higher level perks early in the game in a way that requires some sacrifice. Unlike mods that simply eliminate the level requirements.