Redoing the old studies from the 50's and 60's makes sense. Adjustable speed limits does not: keep the number of driving variables small if you want minimum confusion. For example, reversible lanes are OK if there are physical barriers that shift, but if they are controlled by overhead X or O symbols you are asking for accidents. "Motor memory" of how fast I am supposed to be going along street-type X plays a role in my driving style, and I suspect I'm not alone.
And if photographic speed limit enforcement starts to become ubiquitous, I expect a significant rise in vandalism. Air rifles and slingshots and paintball guns would probably be useful for the purpose.
UPDATE: "Unknown" points out in the comments that the variable speeds can work.