No restrictions on anything. Look at unlimited N/A classes. You won't find a "pure" hemi or wedge. The laws of physics will dictate the direction if the rules are allowed to stand long enough. And, what we're seeing is a merge of the two, each with variations favoring the target class. The ideal 820" cylinder head won't look like the ideal 500" head. It leans toward the hemi end of the scale because it desperately needs the extra valve area and flow. The 500" still looks to favor the smallest chamber as they're hugely over-square and can obtain the valve area needed with shallow angles.
All one has to do is follow the evolution of such classes, and it becomes clear which is best in all out racing. And the answer is it's always a combination. To which side of center the combination falls into depends on the specific class.