Forget An-225 (unless to transport space module), An-124 with 777 engines would be quite impressive.
What China, Russia and Ukraine need is somethings like a C-17. Perhaps they can develop something new instead of keep building older designs.
the An-124 is more possible. The An-225 would never get 777 engines, they need engines with the same thrust as the old one and they should not have more weight
China will never buy C-17, american and expensive.
If they want a heavy Stol transporter they would buy An-70.
I think China will buy many An-124 or produce them