My understanding is that Amazon is backing this. Of course they would, just like all large business support more regulation. They can afford a thousand accountants, the small business cannot. This keeps their competition from the small guy low.
This is how large business keep small business from succeeding, through regulation that only they can afford.
If it takes a thousand accountants, someone has done something horribly wrong.
The store down the street from me doesn’t even HAVE an accountant, and they manage to collect sales tax for one state.
If the law is written correctly, and puts the correct burdens on the states who want to participate, it should be no harder to determine the remittance for all 50 states than for the single state.
I would expect that the feds would set up a clearing house, where all the states would register if they wanted to be part. Any business doing an internet sale that had enough sales to be required to participate would send the address through an internet app, and it would come back with the tax required, and the state online payment location to transfer the funds.
Amazon doesn’t have accountants doing this — their program is already written, and it already knows how to charge taxes for everybody, so if they get a purchase through one of their partner stores they can collect.