While it would be nice to have a 5G adapter option, I don't see a real need for it unless your wanting to shutdown 2.4G in your realm.
The 2.4G Edimax adapter has worked great for me except for the hiccup with V14 driver. No complaints on range or connectivity, and speed is a non-issue. Very dependable running with a 40Mhz channel width. I don't get why people don't like a USB dongle. I mean there are already 3 or 4 wires dangling from the HM, a little USB dongle is not even noticed.
Although, if a cheap 5G adapter existed I would definitely give it a try, but I don't think I'd notice any difference in performance.
The 5G band is more crowded than you think. There are still plenty of consumer electronics devices that use that band. I recently used a spectrum analyzer and was amazed at what was out there.