Carlsen's best FIDE live blitz rating was 2948.
If we stick to classical chess, I don't see anyone breaking 2900 any time soon, but at faster time controls, it's more possible to utterly dominate the opposition and play enough games in a relatively short period to get incredible ratings.
The fundamental reason the blitz rating distribution is wider is that results tend to be more unbalanced at blitz. The easy way to see this is to compare big tournament cross tables. Eg world blitz and rapid championships 2016: the top blitz score is 78.6%, the top rapid score is significantly lower at 73%, and a tournament at normal time controls between the top players in the world would expect to see a lot more draws and a lower top score percentage (mid to high 60s per cent, perhaps?)
"even"