Note that the proposal is about the RMB, not the MMB (the mouse wheel button). What you describe (pressing the RMB opens a MMB pop-up menu) is a known bug that I reported some time ago in another thread (if I remember correctly). If it gets fixed on time, the RMB could be used to activate the alternative dragging mode in Rhino 9.
P.S. I just tested what happens in Rhino 7 when I hold the RMB on the arrow handle of Gumball. Nothing. It’s free for use. This means that the next build of Rhino 9 WIP could include the proposal mentioned above. 
There was also another bug related to the MMB and the pop-up window that prevented the use of pan. It was either fixed in SR39 or I’m no longer experiencing it recently.