Honestly coming up on 18 months in and I'm increasingly realizing I overbought with my M1 Max. It's still blazing fast and I probably won't have any need to upgrade later this year or early next (although I might for tax or other reasons.)
That said there are a few things Apple could do to make the prospect of upgrading more enticing:
#1 More major software that is well optimized for Apple Silicon (especially the GPU and Neural Engine)
#2 Continued major improvements to macOS and APIs relevant to high performance apps (Metal, CoreML, Virtualization, etc) that would demonstrate the seriousness of Apple's commitment to the future of the platform.
#3 Something new and useful beyond just a faster CPU/GPU/Neural Engine/RAM
#4 Mac chips on the same SOC generation as iPhone, or even better, some real Mac first / Mac focused SOC designs
#5 More AAA games on the Mac (I know this isn't a popular opinion, but I'd love being able to game on my Mac more)
(1,2, and 5 are also all things that would make continuing to just use my M1 Max a whole lot better...)
Obviously I'm expecting large general improvements to performance and efficiency with the move to 3nm so that's also basically a sixth requirement.
But I've increasingly realized that a lot of my bottlenecks are at the software level now (looking at you Capture One "Pro") and just throwing more hardware at the problem is either inefficient or just flat out won't solve the problem. I think for me the biggest thing is I need to see Apple continue to show it's serious about the Mac as a computing platform.