As a specialty nitch like for cqb training/police training and in other countries like UK that 7paintball pointed out (shameless plug, they ARE A GREAT RETAILER) then .50 is good for those.
But lets deal in reality people.
After all the different calibers were tried in the 80's (yes I have been playing that long) .68 was found to be the best all around for all aspects of paintball.
For the last 20+ years the standard has been .68 and all equipment has been designed for it. Now your asking players who use modern and stock play to either buy conversion kits (to which some older one will not have) or buy brand new guns/.50 compatible equipment. All of which cost a lot of cash.
I am sorry but this is like trying to change the size of a baseball, hockey puck, or basketball. With the difference is we have more equipment (loaders, mags, guns) to change.
If tippman wants the police/military training and European market great.
Don't try to change the US market