This information is not official.
MDG - the user of Twosim.org forum - is a real one person who have some frinedly connections with brothers Sandisons. As he said - new Boards of Canada album will appear in 2010 absolutly but what month of it he doesn't said.
The some kinda information was on Aphex Twin forum:
One simple clever user said:

"I met steve beckett at the warp 20 party in berlin this weekend and he said boc would be released very soon and aphex not as soon but also very soon

yes I know is not really news but at least its something"

Also has a rumor about name of the album - some people has a dicision that name of next album is "New Clear Down" but it's just a rumors.

Also another good news:

New LP album of Autechre "Oversteps" coming in 22 March on CD and 12''
Tracklist and album covers already exist )