I know this thread has gone on 5 pages and has drifted slightly away from the question that the OP proposed, but to get back to OP's original question -- I'm not entirely sure what the M3 would need to make me upgrade. I've got a 10 core/16 core M1 Pro currently and to be honest, it's really doing virtually everything I need. I think, for many people, gone are the days when one powerful computer was needed. Now, I've got a fast iPad for web browsing, a fast Mac for doing things like large PowerPoint decks on two external displays, and a fast phone for mobile basic emails, small apps and such.
My need for a single fast computer is less important for me these days than it used to be in days past. I remember back in the day when I upgraded my PowerMac Dual G5 after one year to the next model dual G5 because I needed the power. Now, the only reason I upgrade is due to changes in form factor or if one of my kids or my wife needs an upgrade. I don't play games any more, so there's few applications I use that requires top of the line power anymore with one specific exception (Osirix MD), but that application is fast enough on the M1 Pro and it's a small percentage of my total use. I gave my 8 month old MacBook Air M1 to my daughter because she needed a new machine and replaced it with a 14" MBP. Otherwise, I'd still likely be using it.
Unless I need to hand down my current machine to someone else, which is always possible, I'll probably keep this one well beyond the M3.