I am pretty sure that Non-O Family visa is only available where the non-Thai has a Work Permit and the correct visa. Do you have a link stating where DTV family members can get a Non-O this way?
Foreign residents can as they are resident but need a long term visa. Tourists or UK visitors cannot. A letter of confirmation from a pal or relative says "Aye Greg is bunking here for a few days" is not going to work. :-)
DTV_Begpacker You are speculating. Not saying it will not change. You said it "probably" will. How are the embassies going to conduct these background checks for DTV if they do not do them now for other visas?