It's not a done deal: they might mean they support HTML5 websites, not necessarily games. Even if they support canvas, there are unanswered questions which can only really be answered by trying it out: is it actually fast enough to be useful? Does it support WebGL? Does it support the Gamepad API, otherwise how do you detect input? Etc.
Despite that, we are 100% on board to support any consoles which support HTML5 - they just have to have a decent enough implementation that the games run well. If they're software rendered with no way to detect controller input, it would be a let down...