Flew with Air China to Bangkok a couple years back, had a cheeky 60hr stopover in Beijing too. No issues on the outbound flight other than the seats being less comfortable than most. On the way back our bags didn't make the changeover in Beijing, and we're supposedly on the next flight later that night. They arrived the next day (2 flights later), and were supposed to be couriered to us - however they first sent me my friend's bag (who lives in Manchester) and sent him mine! Took a couple of days to get it all sorted and swore I'd never fly Air China again. All being said, these flights are a great price and likely as a result of promotional offers due to their new route via Shanghai to ASEAN. Maybe worth a punt for anyone looking for a (very!) low frills flight to ASEAN, or if interested in a stopover to Shanghai (72hrs entry given with visa on arrival unless they've changed it).
Flew air China last year to BKK, checked bags in at LHR then didn't see them again until Bangkok. Service was great and the planes were clean and new. Went back this year with Etihad and it wasn't as good as air China. Definitely recommend, i paid £330 last year. Transit wasn't to bad little longer than the norm.
Going is possible....but you need the shortest possible return home.
Feel depressed just thinking about a 14 hours stuck in airport and then repeating on way back
December is peak season!