As a footnote, on Sunday I jumped on a half full bus down to Bangkok to pick up my new passport and the journey was no different to any time. There were no road checks or anything else.
On Tuesday morning I was in a taxi heading to Mochit for my return bus and as you do, got chatting to the taxi driver. He was of course from Isaan... knew my area and said that he'd drive me back to Korat for 2000 Baht. These guys must be desperate as this is well under the usual price, and as he was driving nicely I took him up on the offer... with the promise of a tip if he drove 'cha cha'. I must admit that I didn't really fancy the bus with the Covid spike and the bus/taxi in Korat journey combination costs around 400 Baht anyway.
There were no checks at all during the journey back to Korat. Now back home I'm supposed to fill out a form with the local health authority, but when my wife called them about this they said they were busy and would call back later... which of course they haven't. My guess is that nothing will happen.