They can't do anything. They can't search your personal property without just cause. It doesn't matter if they know your name or anything else. They can see whatever they want. Won't matter at all. Are they going to grant everyone $$$ to make their cars comply? They aren't going to do dick. They'd have better luck playing pickup sticks with their butt cheeks. Millions of modified cars, different models, different engines.
The Feds have easy pickings with tax evaders. Much easier and much more to be gained and easier to prove.
You're missing the point. They aren't going to start with the millions of car owners. They're going to start by putting the thousands of performance aftermarket parts manufacturers, vendors, and service providers out of the business. But once they are done with that, they will then come after you - because there is still more money to be made.
What's the point of covering up your VIN tag and pulling the plates off your car if you can't buy parts to make it go fast? Hope you already have a stockpile in a warehouse full of anything and everything you will ever need. Because if this get implemented, you won't be able to buy anything specifically made for a Turbo Buick ever again - except maybe for wheels and stickers.
But I digress, once the parts supply is gone, nobody will be able to mod and nobody will be taking their cars racing. So the drag strips will be closed and there won't be anywhere for you to go or anything for your car to do that it was purpose-built for.