I think (and hope) Apple is going to keep the Mac mini with the M3 and M3 Pro. They already differentiated enough the M3 Pro from the M3 Max, so I see no reason to leave the M3 Pro as an entry Mac Studio. The M3 Max is much more powerful, relative to the M3 Pro, than it was the M2 Max relative to the M2 Pro.
Yes, the new M3/M3 Pro/M3 Max progression is much clearer than it was previously, with the Max being all-round more powerful than the Pro whereas, before, it was mostly just about extra GPU cores and RAM. That would reduce the M2 Pro Mini vs M2 Max Studio dilemma.
That said - I wouldn't completely reject a Mx Pro Studio at a proportionate price - the front ports are good to have and it seems more repairable than the Mini: if you look at the repair manual, most of the ports that might break are on separate boards and, of course, the SSD modules
are replaceable - even if Apple won't let you
upgrade they can be replaced like-for-like if they fail.
The flipside of that is whether the M3 Max is now cool-running enough to fit in a Mac Mini-size case (given that 1/3 of the Mac Studio enclosure is to fit the heatsink needed to cool a M1 Ultra). Since it fits in a 14" MacBook Pro I'd guess that's a yes. That would leave the M3 Ultra to the Mac Studio. I'd be disappointed in that, but then Tim Cook isn't currently returning my calls
Then, there's the question of whether the M3 Ultra will still be two M3 Maxes fused together, or something different (given that Apple have already changed the relationship between the Pro and Max). The M3 Max is already a beast - and the
main reason that the Mac Pro can't have a "max" version is that it needs the second die to provide the extra PCIe bandwidth. Perhaps Apple could go for an asymmetric SoC where the second die was all about I/O (or all about GPU, like the NVIDIA Grace/Hopper).