Is it possible that Branson's ambition has out grown any tie up with SQ short of owning it and you can be sure that Singapore Incorporated (they don't need a FIRB) won't let that happen.
With Virgin Atlantic, Virgin America and Virgin Australia he is very close to have a global airline of his own.
Virgin Atlantic is majority owned by Singapore. I think SQ was interested in
VB a few years ago but the Virgin group refused to give up their 25% veto share. SQ would have had to manage the airline with one hand tied behind their back, so along came Tiger Aus.