There IS no law that says a foreigner cannot open a bank account on ANY visa status. There IS no law that says a foreigner must be present at the time of opening the account (although probably a bit quasi about relevant signatures required).
Each branch manager has complete control over what happens in their branch (possibly with some exceptions from head office).
The branch isn’t breaking any law by opening an account for a customer. They may be skirting a few usual policies if they do but that’s not against the law.
I have no idea why you think getting an agent to open a bank account would be illegal. They offer a service. Much like a customs clearance agent would deal with customs on your behalf to clear an import. You in theory could possibly do it yourself but I guess you wouldn’t get very far if you tried.
I’ve never heard of a bank requiring a TM30 to open an account but many will require a residence certificate from immigration to do so. You do need a filed TM30 to get the residence certificate though.
Really? For everything? Perhaps you need to read posts on different visa forums to realise that there is little standardised pricing across the various immigration offices. Yes for extensions they are standard at probably all offices but as to the cost of a resident certificate or a fine you’d get for a late TM30 filing or 90 day report then pluck a figure out of the ether as to what your local office may charge.
Regardless of what the tax implications may be they would almost certainly be based on 180 days being in Thailand within a calendar year - not consecutive periods.
All will be revealed in the next few months - or it may not transpire at all.
The DTV is basically a tourist visa so it doesn’t offer any advantage opening a bank account.
You can open a bank account on any visa type but good luck trying to find a branch than will let you.
Post in a group local to your location to see if others have been successful. Alternatively pound the kerbs and try and find the one branch that will let you or use an agent for a few thousand baht.
Non O visa (90 days and extend in country if you have the 800k in a Thai bank) does not require insurance.
Non OA (one year from issue) gets you 365 days on entry but you need insurance and if you extend it in country you need insurance from one of the registered providers.