I suppose it's feasible, and I'd be curious to try it with rebels or xp-c/e's just for the sake of doing it, but I doubt there'd be much benefit to it unless you could increase the current to the red/blue arrays. And then you might have heat sinking issues. If the red/blue LED's are driven in parallel, I could see a little benefit (especially in beam quality) to swapping in a single high power LED for the 3mm/5mm/whatever arrays.
I'd be more curious to see an upgrade to the primary LED, especially in the white-only model with the bigger reflector.