Some Clannad fans are tough to please. They complain for a year demanding a dub or dubs in general from the company, then at the first sign there might be hope, they aren't satisfied.
Sentai has always had the position if their sub-only titles do well, they might consider dubbing it... depending on the viability and demand. If it sells well, they may consider it. If it's a niche or expensive production on a risky title they'll take the conservative position - Matt Greenfield talked about at Nebraskon 09 in the late fall, about dubs while increasing sales are not often enough to make a release profitable.
At ACEN 09 Matt Greenfield said: http://www.animenewsnetwork.com/convention/2009/anime-central/adv-films-and-sentai-filmworks