Since quite a few people have posted in certain ways that seemingly indicate hints to their role, it could be advantageous to look at who is likely in the remaining groups:
Ok, so I am assuming that the G8 people will come from those not having permanent seats on the security council.
Security council: China, France, Russia, US, UK (two remain)
Remaining G8 (after SC members removed): Canada, Japan, Germany, Italy (one remain)
Then, the three for the G20 depends on whether it is the G20 Major Economies or G20 of Developing Nations. Three major players are China, India and Brazil. But each are kinda for reform. Then you have to throw in Australia, UAE, Saudi Arabia, South Africa, Mexico too.