They have discussed implementing/enforcing taxation on tax residents of 180 days plus.
However no official procedure is implemented yet.
Anyone registering is doing so voluntarily and they do not have the system in place yet to process.
It is a wait and see at this point what , if anything , comes of it.
They are after those hiding global income, many rich Thais and foreigners with overseas money taking advantage of a loophole that is supposedly closed now.
Money being brought in , may be subject to tax regardless of whether it is not in the same fiscal year.
Because they have a reentry permit, they will likely not be allowed to enter on DTV.
You cannot "switch" visas like that.
As the DTV is not activated, the nonb still is in effect with the reentry permit.
If the work permit is already canceled and you did not cancel the extension, then your reason to stay ended the day you stopped working, you may be subject to a hefty fine.
Should have canceled the extension before leaving Thailand.