Agree. For me the screw clamp is great and for my purposes the head is perfect as is, but for those who are seriously into panos the D4 is lacking one key feature: a properly and fully marked degree scale. It has a rudimentary scale in what appears to be 5° increments, and my D4 with Arca screw clamp does have an index dot, but I guess it would be a bit of a pain counting 5,10,15 etc as opposed to something like the RRS or NovoFlex, or Cube that have all the numbers marked to 360. I believe this is why the guy on the German forum got out his drill and got rid of Arca top pan completely (not just the clamp), and it might be why Buckshot was asking about PCL-1.
As far as the quick release question, I think it'd be pretty easy to change out the Arca clamp for a Really Right if you really wanted to. Looks like a 3.5mm hex wrench would do the job. Pretty sure it would be just like the hybrid Cube in the link. I had planned to do exactly that, but now I like the Arca classic clamp just fine. I use a RRS 'L' bracket BTW.
Here's a pic of the D4 with only the clamp removed, as opposed to the other pictures that show the whole top pan removed. The only remaining question is how well that little post fits the recesses in RRS clamp.
As a D4 owner and previous user of RRS lever clamp, I'd recommend ordering with classic clamp.