Why would it not be possible, it's just a 4 stroke engine. As John said though, it'd be much better buying an R1, then turbocharging that. I bought my R6 more for the handling (and the chicks ) Damn my GF just read that too...
Cost would be the prohibiting factor.
I think a turbo on an R6 is better than going for the liter bike.
1.) Its unique
2.) You retain the agility of the R6 over the R1
3.) The increased power. You could change your gearing for a bump in your top speed and to also reduce the amount of power on the lower gears. Dont want the bike coming up on you too easily.
4.) Friends dont let friends get swingarm extensions.
Id love to put a turbo on my R6 but I think Ill pay it off first