OH trust me i know alot about niche markets and marketing... Its what i do for a living, i work at one of the biggest marketing/ad agencies in Chicago as an account executive of interactive marketing...
It would completely work. AND it would be something that would bring alot of people in. Its actually something people do on a daily basis... which is why i had to bounce it off my friend... and we both looked into it. Its yet to be done.
I don't even think 'niche' is the right word for it...