I doubt that there will be any new M3 device.
This is mostly due to the fact that TSMCs N3B was not what everyone hoped for. Problems all the way, low yield rates with wavers.
N3B yields are likely no where near as 'horrible' as folks on. 1.5 after volume production there should have been improvements.
Pretty good chance this is little to do with fab processes and far more to do with just generally relatively higher costs for much bigger dies. Couple that to the relatively much lower run-rate volume for the Ultra (or bigger) class of systems it gets worse.
There is also no place else for the Ultra to go. There is no "hand me down" product to shovel them into. That isn't a path to 'churning' the biggest SoC package and 'throwing it away' every 12-14 months. Nobody in the rest of the large package business does that ( Intel , Nvidia , AMD , etc. )
Pretty good chance the largest die is going to get onto a M(n) , M(n+2) , M(n+4 ), etc. pattern. So M2 -> M4 --> M6 .
Apple relatively quickly dumping the M2 Max out of the the MBP 14/16" likely just made things worse for a transition off of M2 for the rest of the products using that building block ( Studio and Mac Pro). Now they have to shoulder a larger share of covering the investment/R&D/etc.
iPhone SoCs come in and the phone gets sold for 3 years. In no way shape or from doesn't Apple completely drop the latest phone SoC in 12 months. It is sold for at least 4 years via other 'hand me down' routes through plain, entry iPad , AppleTV , etc.
What is relavent is not just when it comes to market for the first time. When it goes out (gets dropped) is a very significant issue also. The Max class die is 400+ mm^2 chip. Dumping that in the 'trash can' after just 12 months of retail would be very expensive.
The other issue is that Apple is reportedly not going to split the iPhone SoC across fab processes this year. The 'plain' and Pro iPhone are reportedly going to A18 (and A18 Pro? ). That is a demand bubble that could squeeze out M-series for a relatively new fab process that has longer 'bake' times.
So why the iPad Pro got the M4 in N3E first? Because the sales are rather low compared to most other devices from Apple, means its better suited for a controlled start of N3E production.
Yields with N3E are way better.
Also because the M3 wouldn't work with the iPad Pro screen. Apple's display controller has been behind the curve for a while (e.g., ignoring DisplayPort 2.x ) . They chose M4 to merge that in.
So whats the next device to go M4?
I bet it will the the iMac which is still on M2.
Mac Studio might be, but i would not expect this before fall.
Mini / Mini Pro can also 'sop up' M2 gen SoCs for bulk of 2024. ( again the rapid dump from the MBP's ; MBP 13" was 2nd best selling system. ).
Pretty good chance Apple is still felling some urgency in MBP space so those iterate out also in the Fall. (and M4 , M4 Pro available for Mini).
The hang up for the Studio is possibly hung up on the Ultra. And the Ultra couples the Studio and Mac Pro together. N3E has incrementally better yields , but it also tosses some density to by that. ( all the caches/SRAM get bigger. And biggest Apple M-series dies have the biggest cache area. There will be area increase creep there. They can work on trade-offs; smaller logic for larger caches. ). IF the "Ultra" dies creep up larger than the reticle limit then the packaging tech they used previously ( InFO-LSI ) doesn't work so well. CoWoS packaging tech has been swallowed up by the AI mega package hysteria ( huge backlogs ). If Apple has to switch packaging or go mega-monolithic that will probably be a time hiccup (if not originally on the roadmap).
As the next TSMS itteration N3P will be just a shrinking, dont expect the same huge performance benefits as from M3 to M4.
But if you are talking big dies that are on edge of busting the reticle limit... shrinking might be necessary. The Max die was already skirting the limit when paired up. Apple designs are abnormally cache heavy. The compromise that N3E makes is impactful trade-off ( it was not 'free' fix. )