Why not start by building a landing page and seeing if you can get at least a few hundred people to sign up? Seems like a much easier way to determine if the market's there than diving in head first.
Honestly? Because if I can't sell it, I'll give it away, its something I badly wish existed for my mum over the last few years so if I can't make a living on it I'll host it for free and fund through my current business as a donation.
