I've often wondered what the best way to do this, if the goal was to bring over only top tier talent. I've heard it floated it could be a bidding system instead of a lottery (countered with the fact that only the biggest firms would be able to bid high enough to bring people in), but I'm not an economist so I don't know how that would all shake out.

I think I'm more just speaking out loud here: what is the optimal way to do this that allows a capped influx of talented outside workers, that doesn't allow "degree mills"?

I don't have an answer, but I honestly wonder. Some of the green card folks I've worked with (I know that is different, or at least I think it is in the grand scheme of things?) have been some of the smartest people I've worked with.