Some parts of the west already did that years ago in electricity production. For example carbon free electricity production shares in France (88%), Sweden (98%), Finland (90%), etc.

Though there is still a lot of work to do to go fully CO2 neutral due to cars, trucks, ships, planes, fertiliser production, etc.

My concern is that, since it's harmful to the planet and they're on track to be the largest economy, their absolute coal output is more relevant to the rest of the world than what percentage of its respective GDP it is. I don't necessarily blame them since their main priority is their own growth, but we're relying on their good will in 2030 without any way to enforce reduction if they change their mind.

Complete non-sequitur. OP said "China is building nuclear", not "China is building more nuclear than wind/solar".