Coal plants can be fairly easily repowered to natural gas, which decreases CO2 emissions but more significantly drops local particulate emissions nearly to zero. China's air quality is famously poor so this would be a smart move.

China still needs baseload generation and converting coal to NG is far cheaper than nuclear or advanced stack scrubbers.

They are, but you still need baseload. Solar and wind are great — when it’s daytime and/or the wind is blowing. Coal (and natural gas, hydro, and nuclear) can provide more scalable power on demand. These fill in the gaps for times when solar and wind production are lower.

But China isn’t likely to convert existing coal plants to natural gas. If they wanted to do that they could do it already — they have an LNG pipeline from Siberia. But instead of replacing existing coal power plants, China keeps approving new ones — it was reported last year they were approving two new coal fired plants per week. So even if they increased their LNG imports (they’re looking to open a second pipeline with Russia on the western side of the country), those coal plants aren’t going anywhere — with the rate they’re building new power plants, they’re not likely to be “upgrading” any coal plants to LNG anytime soon — they’ll just build additional LNG plants (and likely further coal plants) alongside those existing coal plants instead.

Not in the least it's the most effective means for shipping methane across such distances. LNG remains liquid across the voyage, and any boil off is used for the ship engines that do not typically use diesel.