The question is, is the quality of the correction also impacted with less channels used (for example because there aren't enough filters for the system to use)?It is worth keeping in mind that the less powerful Storm units limited the number of "support" channels, to keep it within the processors capabilities... the flagship models have no such limitations.
I don't even have one channel that is full range, I have a sub-sat-system crossed over at 80 Hz because the speakers can't really do much below that (XTZ M6) but I have 3 subs. I'm still very interested in ART. I suspect ART could still bring noticeable improvements with only the subs to work with. If I could get ART, I'd probably buy a fourth sub and maybe even switch my S5 surrounds out with M6s if that helps (no idea if ART can do anything with the main speakers if it can only use them >80Hz) to give it more options. Frankly, I wouldn't want to use ART with my main speakers anyways since I wouldn't trust it to know the limits of my speakers and I don't have enough amp power for that application as well. I'd rather just make it use my subs, which already have capable limiters built into them, so I don't have to worry about overdriving anything...So the version of ART deployed on individual AVR's may potentially be limited to a certain number of "support" channels, although you may be able to choose which channels are supporting and which are not.
For most of us out there, having 13 channels would be more than ample - and looking at actual implementations of ART by current Storm users, often even the 2 mains and a sub can make immediately noticeable improvements!... personally I would hope for 6 channels of support - which at just under 1/3rd of the channels the basic Storm AVP supported, should be viable by the Denon X800 series and competitors. Why 6: I have 4 full range speakers capable of going down to under 30Hz, mains L/R and Surround L/R + 2 subs... my height speakers are severely constrained in the bass, my front centre goes down to 40Hz in theory... so could potentially be a 7th channel - still even at 7 channels, that is 1/2 what the more limited Storm unit supports - so should be viable!
I know for a lot of people, this is not what they want to get ART for, they have huge, capable speakers with lots of amplification behind them in addition to multiple subwoofers and sure, in those applications - especially if it's in a dedicated, already well treated room, ART will probably be able to get the most out of a system but I suspect a lot of people also have a use case similar to mine. If D&M and Dirac want to roll out ART for the Denon X800 line, it has to perform in non-dedicated rooms, with less than ideal speaker placement and count, often in an unsymmetrical layout. So my biggest question is, will ART be able to bring significant improvements in such conditions or is it only usable in "good" rooms..?