If they can't keep up with custom hardware then somebody else is going to build it. What's more because AI is a technology that by design is going to consolidate into a few players who have access to training data (google, Facebook and maybe Apple) you are going to have companies so huge they are just going to want to make their own chips.
You've got these companies that a few changes in who makes the chips could drop their value by hundreds of billions of dollars. And you have investors buying in during those high-valuations.
I don't think AI will go away, the ability to replace paying wages is so valuable to the billionaire class that it's going to keep getting pushed, but I do think that it's likely that a bubble will burst and of course when it does it's going to screw over working people because it always screws over working people.
Plus we all know we're going to have to bail out the banks that wound out all the money to these AI startups because if we don't when they go down they take the entire economy down and us with it. And we're too much of a bunch of pussies to just nationalize them however briefly