I guess MAN-IAH is interesting, as while SQ almost certainly cannot get a London-US route, MAN-IAH opens up UK to US to SQ, and they might see this as a satisfactory alternative to DME and London for now.

And MAN is easier for many to connect than DME in Europe, due to Russian Visa issues. (please correct me if I am wrong. I know that DME can transit, but if on separate PNRs, this may be tricky? And Moscow has more than 1 major airport so flights may depart from the other one, and you probably need a Visa for the change of Airport)