UPDATE: Looks like it'll be a Charles Schwab, not McDonald's. Whew!
I hinted yesterday that there was a big chain-related scoop in the works, and here it is: There's a very high probability that 100B Seventh Avenue's next tenant will be McDonald's. I say this without ultimate confirmation because the source was a worker inside the space (as opposed to Corporate, which was unable to comment), but in past experience contractors tend to be trustworthy sources.
The space, which is on Seventh between Union and President (where Kaplan tutoring used to be), is certainly large enough to hold the Golden Arches (it stretches back pretty far). Big chains have traditionally held off on coming to the neighborhood because many storefronts are too small to accommodate them, but that doesn't seem to be the case here.