Huh. I like the idea of lands affiliated with particular strategies, and the concept of 'locked' abilities. But my immediate thought is that this would be really similar if it said "whenever you cast an instant or sorcery spell, you may pay 2U. Are there other ideas for unlock that make it stand out more?

Sure. This was just the first one that sprang to mind.

I'll note that this is somewhat similar but also very different from a trigger.

Not really feeling the unlock trigger being an untap clause, but getting access to cooler and better abilities on a trigger is pretty cool. Feels a little like Transform (in terms of design principles and space), but the change isn't big enough to warrant a whole extra card.

Well, it's mainly a rough concept card to show something that can be done with lock/unlock. The way the trigger functions right now means making the draw a tap ability makes little sense.

(Also I have to admit a weakness for .)

By the way, I imagine this would have a slightly altered card frame, with a two-tone text box: the bottom portion would be darker, with a line across it that would have a key hole in the middle. The text "[locked]" would not actually appear.

Yeah, that's about how I imagined it looking.