I might have to do a local survey, but in the 24 years since we moved to this area of southwestern Montana (about an hour from where I grew up) I've only run into two .264's users. Well, three if you count me--and I bought my first .264 from one of the other guys!
I do KNOW, however, that the .264 has made something of a comeback in the past decade. Published my first article on it for HANDLOADER in 2005, when there was very little current handloading data, and none with newer, more appropriate powders--so literally had to work up my own loads, using a combination of case-head expansion and chronograph results.
After buying my Ruger I found a LOT of current data, with far more powders, and only a year after doing a write-up on all of that, find even more data available. Plus, my Ruger has a 1-8 twist, considered much more appropriate for 6.5mm rounds these days. No doubt Ruger used that twist because they were also using it in the 6.5 Creedmoor, but it's also an indication of increasing popularity.
Though I doubt the 6.5's have increased significantly in popularity among most hunters, who still buy a lot of .243's, 25-06's, .270's. .30-06's and .300 Winchester Magnums. A lot of rifle loonies have a somewhat skewed view of what's popular, since we spend so much of our time among other rifle loonies!
