They still hold power over multiple cultures and ethnicities and brutally suppress secessionist movements.

That's literally every country on Earth. That's what countries are. The project of nation building is welding together different ethnicities and cultures into a single unified nation, and sometimes that requires putting down secession to maintain cohesion of a single state. If your definition of "empire" basically defines all countries as empires, it isn't very useful.

I actually think the future will be bipolar with India and China as the competing powers. The west has had its time.

The West won't vanish either, they're still going to be very powerful competing powers. It's likely going to break up into chunks, though, starting with the split that's emerging between the US and basically everyone else. Then, maybe, Europe will fracture further into blocs. No idea what Canada is going to do, probably get invaded and absorbed by the US or something.

It's going to get ugly and strange. But, in that ugliness and strangeness, there will finally be space for revolution again.