I did a mod to one about 2-3 years back using the uncut MJLED and its output was increased. However, it does not compare to some of the small lights available now. Part of the reason is that its regulator does not put out that much current. Also the funky optic makes getting a good beam difficult.
It is nowhere near as bright as a Fenix E1 modded with a Seuol SSC. The E1 can run about 5 hours at amost perfect regulation on an Energizer Lithium AAA with a pretty impressive output.
I really do like the UK2AAA form factor. I think that maybe one of the soon to be released Nichia LED's may make the mod worthwhile. They are supposed to be about 2X as bright as the current CS Nichia. Should give decent output and fantastic runtime. Who knows, maybe UK will release an updated version - I'd buy that.