True. I still doubt it will ever be worth their while to go after individuals for a 10 year old ebay purchase though.I've always assume that anything one does online can be tracked and accessed, certainly at the surface. Privacy doesn't exist online. So that possibility is real enough. And if there's a revenue gain, there's motive. We'll see.
Even if they did, can you image the uproar from a couple of million constituents getting a retroactive tax bill in the mail? Especially considering that many of those people will be in the lower "poor" classes of people.
They'll be talk of exemptions and "fairness" because "rich" people buy high priced items locally and "poor" people buy cheap goods over the internet. It won't be fair to stick "poor" people with a retroactive tax bill.
I think any politician would correctly see retroactive enforcement as a political disaster.