I don't think it's a matter of paying or not paying a fee. The purpose is not to collect revenue but to allow ATC (especially for flights that cross an international border) to code the aircraft on flight plans to yield reasonable performance expectations. ( ICAO is made up of contracting states, that is, countries, not manufacturers, and that's why it's a UN agency.)
For example, the A&S18A has been out of production for eons, with nobody to pay any fees, but it's in there with designator UM18 (from Umbaugh, the original promoter in the early 1960s).
If you need something to enter on a flight plan, there is a provision for microlight gyros (which covers most EABs) to use GYRO, and for as yet un-designated aircraft to use ZZZZ.
I suppose Abid could ring them up in Montreal and get it added if he has the time/inclination. There's a phone number and an e-mail address on the website.
The issue is likely that there are not a Significant Number of AR-1's that are Requesting Air traffic Service.
How many people file Flight Plans when the plan is to stay within 20 miles of the airport?
What got me thinking about this in the first place was when I was adding a profile for a FW that I will be using next week at an accelerated school in Florida. The CFIs always want you to contact 1-800wxBrief. When you add a profile on that Website, it asks for the ICAO designation. Since, I am seriously thinking about an AR-1C as my end-game, I wondered what its designator was...