I'd expect they sound very good... the Mark Audio drivers have a fairly loyal following on diyaudio for those that prefer full range drivers... my worry would be the ability to reach reference levels for home theater with sufficient battery life to last through a long movie. They state 'up to 10 hours' of battery life, but I'm guessing that is at low volume levels and optimistic at that. No big loss for HT I guess, as the alternative is... wired speakers, but I suspect the target market is those wanting the minimalist look, and power cords are tougher to hide than speaker wires... much less tougher to run.
I think sound quality at modest levels would be excellent, and would blend very well with a sub crossed at 80 Hz... the problem is how many people willing to spend $2.5K on a 5-speaker set are willing to 'settle' for 5.1 surround? Nice idea, likely very nice sounding, but I suspect the market is pretty small at that price. Get them down to $200 per speaker and that might change.