IAH-MAN never made much sense. In addition, flying SIN to IAH via MAN or most places in Europe adds more than 1,500 miles to the great circle route. Flying via somewhere else in Asia would be much more direct.

SIN-SGN-IAH would be interesting, if SQ could get fifth freedom authority, given the sizable Vietnamese population in Houston, except the 350-900ULR is too premium heavy (67 seats in biz with only 94 in economy) for those markets.

SIN-ICN-IAH adds only one mile to the great circle route, wouldn’t require an ULR bird, and would fill in a gap since neither OZ nor KL serve IAH, but could SQ get the authority to fly that?