While I agree that AMB could be a way to push the clients toward the higher standard hotel (and presumably, the more profitable, though it's not certain, 3-starred Michelin restaurants often have lower margin than a kebab joint), I am not certain that it has lost its use. While you point out that the upscale offering of IHG has increased, something I agree with, I'd reach the opposite conclusion. There is an increased offering of upscale hotels, in new destinations, so the effectiveness of having a system to push returning customers toward them should improve, shouldn't it? They'd need to strive to increase and harmonize AMB benefits to their whole luxury segment to achieve the same effect (also, I wouldn't put Indigo/Voco in the same segment as Kimpton and IC...)
I mean, I also think they'll move toward more integration of the systems, but not because of reduced ability of the AMB programme to drive customers toward the higher chain.
We don't really know who the AMB are and what their travel pattern is. I am not sure a lot of the HIX/HI/CP customers would say "mmm, I could get some benefits from IHG One by electing to stay at an IC instead of say a Hilton, but if I pay 200 USD more I can get more benefits..." For a single trip, like a vacation, it's not seem to be worth it (not everyone do the calculation we do on this board, I think we're not typical representative of the hotel stayers in general). I think the AMB programme is a draw for people that would like to secure benefits (and the instant Platinum thing was also something that could be worth it for people knowledgeable enough of the system to stand in for a status match... starting at platinum instead of starting as a nodody can be a draw if you intend to stay a lot in ICs). Since it pays over time it's more sensible for people to shell out the money if they are frequent upscale hotel guests already.
But I know nothing of how hotel marketing work, so I could (and I am) certainly missing a lot of things.