It is. Making a new chip is very very expensive, but copying it is cheap. People demand millions of low end systems but only thousands of high end.

What companies do is use mass production for lowering the price not only of their low-end chips but high end too. They just disable and don't test the "advanced features" in low end cards.

With drivers you could enable it. Some blocks could be damaged(as it was not tested) but as a much lower price you just can buy new cheap ones.

It is relevant; people are "softmodding" GeForces into Quadros, theoretically costing Nvidia millions in revenue. Open-source drivers might make this even easier.

Do you have more details about this? Maybe a link or something.

They typically laser-cut traces etc nowadays.