I don’t believe AAF has a license fee. See:
https://amwa.tv/developers.shtml
Developers have access to specification files, sample files, reference files, and an open source effort underway, also SMPTE ratification, etc.
AAF has been an open standard for many years.
Licensing from Avid is around development of DNxHD in a product and the ability to call it DNxHD versus SMPTE VC3. So there is a license fee for the Avid Media Toolkit (AMT) with DNxHD, etc. that many vendors have adopted – for example Resolve and Redcine X Pro’s direct export of AAF. and MXF wrapped native DNxHD media. Same for camera and external recorders, etc. But AAF on its own does not have a license fee. There may be confusion that Avid started AAF as an extension to OMF 10-12 years ago, but many vendors are part of the organization, and anyone can join, vote, extend, etc.
Michael