been using a CLion quite extensively for last few days and have to say I really like it, and decided to stick with it.
so, for one of my open source projects (MEC) I applied for an open source license, and they granted within a couple of hours , effortless/painless very simple form to fill in, definitely worth the minor effort involved 
(you get a full toolbox license, so all products including IntelliJ/CLion, valid for a year, and you just re-apply at end of subscription)
basic process is, get the Project Owner/Lead to apply, they take a look at your repo/license etc, and then it seems they will then grant a number of licenses for āactiveā contributors.
for active contributors, one thing was a bit unclear, it looked like with my project, they only looked at the active/default branch (probably they just use the GitHub insight page), as they didnāt count one of my contributors, who has been working on a separate branch. though, Im sure you can probably discuss this with them if necessary.
(though, I can just merge his work, which was planned anyway⦠then ask them for an additional license)
anyway, hats off to JetBrains for supporting open source projects 