Moving the battery into the skidplate would be a huge step forward, as would a set of quick release electrical connectors so that the rear subframe could be easily removed to work on the carb. A titanium rear spring, would be great, and so would a little more bling, like maybe some black wheels or a limited edition wr that came in yellow or white. Kawasaki is hiding the fact that their new kx450 weighs ten pounds more that last years with little more than colored triple clamps and pretty black wheels. EfI would be nice for the wr, but not if it came at that cost.
EFI will add weight. Some sacrifices will have to be made if you want EFI. I currently own an 03 WR450/SM and even with all the crap i have stripped its still a pig!! The wonderful starter problem is plaguing the bike currently and it really sucks roll starting it(kicker shaft broke).