I'm okay with Fletcher's approach, frankly.  Yes, there are relevant qualms about calling it a "mosque" since that's not all the planned center would be, but there would be facilities for holding prayers and services, and really the distinction between mosque and prayer room in this sense is a semantic distinction.  If there were a line in the first paragraph of the lead qualifying that it's not solely a mosque project and perhaps even the word "mosque" isn't strictly correct, I'm okay with the use of that word in the title.  But it has to say "near Ground Zero".  NickCT's comment about how WP:COMMONNAME should be the sole arbiter of this matter I think doesn't recognize that there is a spirit to the rules that trumps the letter of the rules.  Wikipedia is not a place to spread misinformation.  Calling the page "Ground Zero Mosque" despite the fact that the term misrepresents where the mosque facilities will be, and despite the fact that reputable sources are choosing not to use the term because it misrepresents where the mosque facilities will be, flies in the face of the idea that we're supposed to be reflecting what the WP:RS sources are saying.