So I know that when you download some DLC it's locked to the PSN account the PSP is registered to, but since we have the kirk keys, what's to stop us from using them to decrypt them and patch them to run on any PSP we want?

What specifically is the mechanism that stops you from running it? Is it different on a per-game basis? I imagine it would require you to identify some kind of hardware ID of the new PSP if you wanted to use the DLC on a different system.

But if it is actually managed on a per-game basis, that could make it impractical to do so as it would likely require a different method for each game. Personally I'm interested in this so as to play outside of region DLC with Dissidia 012 Duodecim