Canonical has confirmed that proprietary driver support will be required when the X fallback will be removed.

It's been rather unclear what will happen after Ubuntu 14.04 LTS is released, especially because Canonical said that it would remove the X fallback support by that time.

One of the Canonical developers has answered a question from a concerned user that was curious about the Mir progress and the lack of proprietary driver support.

“But what happens when that fallback is removed in 14.04 LTS *if *AMD > / Nvidia have not released proprietary drivers? Will we still be able to > use the drivers they supply now?” asked Kyle Williams on the official mailing list.

The answer came from Canonical's Kevin Gun, “Hope you understand it would be inappropriate to discuss partner commitments. But, yes, what you asking is technically correct in that proprietary driver support would be required when there is no fallback.”

This means that Canonical is fairly certain that they will manage to secure Nvidia and AMD support, by the time Ubuntu 14.04 LTS is released, in April 2014.