In theory, no businesses should have to close if what they are proposing goes through - they're not making modifying illegal.
From my understanding and a bit of research it seems what they are suggesting is that cars that don't meet original type approval will require an IVA test - which most well built cars should go through anyway. Secondly, it seems the MoT tester will be the one that determines whether a car needs to go for that IVA test, which again shouldn't be a problem for most of us.
It would take a massive investment to make it work, which is why personally, I don't think it ever will. You never know though!