I don’t think it’s only about exclusivity.
Implementing ART into Marantz, Denon and other AVRs isn’t trivial and the computing power of those AVRs might not be capable for ART on all 11.4 channels that some Denons and Marantzes have
As demonstrated on the Storm platform, when implementing ART, you can choose how many speakers to allocate as "helpers"...
So in addition to the normal Dirac Target curves which apply to all speakers, there is the allocation of speakers to the "helper" role - and the smaller Storm AVP, is apparently limited to 10 helpers, due to processing constraints.
Once this is clear, then we can make some educated guesses...
1) Dirac have told us that if a processor can handle DLBC then it can handle ART... so that gives us an immediate indication on which AVR/AVP's will be sufficiently capable
2) Manufacturers can limit the number of "helper" speakers, so as to limit the processing load
3) We already have multiple user reviews of systems with fewer speakers (down to 2.1) showing that substantial benefits acrue from ART even when using fewer speakers
4) I would be very happy to see a setup limited to something like 7 helpers, perhaps at a more economical price point...?
Key thing is - an AVR/AVP demonstrably does not need to be capable of using 11.4 channels with all of them as "Helpers" - and at least one model from StormAudio, demonstrates that by being limited to 10 helper channels, even when using 16 channels.