Before flaming this suggestion, you have to understand that it would be a radical change, and would require other radical changes to every perkline in order to make sense. Please don't come in here and say, "but this would make perkline xxx useless and perkline yyy OP," based on current perk actions.
With no further ado:
What if using a perk action didn't just lock that single perk, but what if it locked the entire perkline? In other words, you'd have to choose which perk action from a given line you wanted to execute. I think this would take away a lot of "piano perking" and replace it with some careful thought in choosing what actions to use and when. You know, strategy, rather than button mashing. Kind of like the way that FA and AS are going to lock eachother, making you choose which one is more appropriate for the situation.
Obviously, a whole lot of perk actions would need to be redesigned. It wouldn't make much sense to have 2 DD perks with the same evade check in the same perkline. But you could have, for example, a perk with a large DD and a high evade check, alongside a smaller DD perk with an easier evade check to land. You could have a perkline that makes you choose between buffing your own evades and debuffing your opponents evades. The possibilities are endless, but the story is always the same: we get to quit pressing every singly button we have as soon as it lights up in pvm, and we have to think harder about what's really important to use in pvp.
This would also probably be a step away from strictly alpha-based combat for some professions, because in general people would have fewer DD perks. I think reducing the effectiveness (and dependence on) alphas for some professions is one of the original goals of the whole rebalance shebang.