If you use your dtv correctly you would be spending up to 180 per annum and thus not be a tax resident. If you do not (meaning you are not really a nomad anymore) and extend which is possible at the discretion of immigration you would then be a tax resident and file a tax return but that does not mean you would be paying a lot of tax. There are tax treaties between countries to avoid double taxation and in Thailand the law still only taxes what is brought into Thailand so all in all not a big risk; the bother being that you need to file a tax return and declare all that you have worldwide.
if you are in Thailand more than 180 days you are a tax resident and have to file returns with the tax department so it can assess what it is that you may need to pay.
it is also the only visa in the world that forces you to be somewhere for an indefinite period of time preventing you from traveling and going about your business.
the system makes no sense. That is why it is so difficult to comply with. That you should prove that you are not in Thailand is one thing but having to prove, for nomads, that they are effectively sedentary and are not moving is incoherent and borderline s.
So I gather you applied for it from outside thailand and decided to go to thailand before receiving the visa. I thought this was not possible or is it?