A few thoughts on this.
The Mac Pro / Mac Studio will see upgrades happen when the M3 Ultra is available. They are not going to launch these with only the M3 Max edition, then bring Ultra along later. Too many people will hold off for the Ultra version. Also, from the benchmarks I've seen the M2 Max MBP was a bit faster than the M2 Max Studio. Also, most people with the M2 version of the Studio will not be looking to upgrade anyway.
I would be the timing on this is much more related to the N3B line at TSMC and the available capacity. They are currently running A17 chips for the iPhones, but have some spare capacity. The MBP runs will be low enough quantity that they can get these chips out and give reasonable shipping times. However, if they went full bore with the M3 MBA line, the demand would cause problems.
Longer term, I can see them moving towards a schedule where the premium chips drop in the fall in the pro lines, with the 'consumer' lines hitting in the spring. People that want to be on the cutting edge will usually pay more and buy into the pro lines. Just makes sense from a business perspective.
The M3 isn't a good upgrade for everyone, but I'm still running a 2018 i9-8950HK w/ a Vega 20 MBP. Just ordered the 16" MBP w/ 64 GB of RAM. I need it to run Unreal Engine to create builds of a game for iPhone. I'm ecstatic about this release and the timing.
One last thing, this talk about the M3 making the M2 useless is ridiculous. The only thing this makes useless is the bragging rights for M2 Ultra owners. Their equipment will still do all of the same work it did yesterday, just as fast. Technology will keep advancing and timing your buys is about certain key features that help future proof. For me, it was HW support for Ray Tracing, which is why I had not upgraded to the M1/M2. Also, complaining about things moving too fast is again just about bragging rights and people wanting to feel special. However, if I buy every 5 years, I'd rather see 5 iterations between my last buy rather than 2, just means that much more improvement between the two.