I'd say 5 of the 6 teams are the Force, Kuala Lumpur, Shanghai, Hong Kong & Singapore - given Twiggy's mining connections.
The other that takes it up the 6, and the third than accounts for the "quickly expand to 7 teams" is the big question.
The Japanese Top League season runs from Mid August to Mid January, so there is definitely potential interest there, especially with there being no overlap in seasons.
I very much doubt Papworth & Co. would want the Rams competing in a competition that would be played alongside their treasured Shute Shield. It makes no commercial sense unless TwiggyRugby is played on a Wednesday, and that makes no sense for TwiggyRugby itself.
The Fijians would definitely add a competitive element to the competition, that's for sure. Although considering they don't really sit in the "Twiggysphere", I doubt they'd be involved unless WR were to extend their NRC funding. Ideally you'd want involvement from all 3.. (Japan, Pacific Islands & another Australian team)
I'd actually put my money on Colombo being lucky number 6th.
Japan, Fiji & the Rams don't make much sense logistically or contractually for their respective owners & unions.