I too think it will be a long time before they mess with the 7,1. 5-7 years would be my guess.
Well, the 6,1 went 7 years without a single update (apart from dropping the entry-level model and re-shuffling) so that would hardly be surprising

Really, arguments about pricing notwithstanding, that's the main reason why pro users are likely to disregard Apple - the last
two Mac Pros have been left to whither for years (the old Mac Pro tower was actually discontinued in Europe ~2011 because Apple couldn't contrive to fit a fan guard to meet a regulation that had been pending for years...) and then belatedly replaced with a radical (and more expensive) re-think that demanded a major workflow change and re-tooling. Not much action on the iMac Pro front in the last year or two, either....
Apple has 500+ stores, 130,000+ employees and $3 billion a month in operating expenses they’ve got to cover. Their net profit margin of about 20% pales in comparison to other companies.
So what? Someone hand Apple a violin. If that means that Apple has to sell a 1TB SSD module for 2-3x the price of a comparable, top-end 1TB M.2 NVME stick (which is more complex as it includes a controller) then that's Apple's problem, not the consumers.
Of course, the only reason that Apple would put up with a "reduced" 20% margin is if having all of their own retail stores, buying up lots of tech companies, designing their own processors etc. means that it is 20% of a
much bigger pie then they'd have otherwise.
We're talking
retail prices here - someone has designed, BOM'd, manufactured, tested, distributed, warehoused, promoted, advertised, billed, delivered etc. that M.2. stick too, and been paid for it - in fact, Apple should have
saved on that process by having so many of those steps "in house" and eliminating an army of middlemen.
Sure, Apple has some expensive products. But they’re not overpriced, are they?
Yes. $300 for 1TB of SSD (including controller) is expensive. $600 for 1TB of SSD (without a controller) is overpriced.
To be fair, HP, Dell, whoever will also gouge you for branded BTO upgrades but - certainly when you're talking about tower PCs and workstations - at least you have a choice of using standard parts, and their base configs are usually more generous.
Apple have plenty of expensive products (MBPs) quite a few reasonably-priced products (iPads, even the 5k iMac provided you
want $1000 worth of display built in, use external storage and buy your own RAM), then there's the Mac Pro itself - which seems to be the first personal computer ever designed
up to a price so you can argue over whether it is over
priced or just over-specified and over-engineered.
...and Apple decided not to use M.2. slots. A major point of integrating all sorts of functionality into the T2 chip
should be to reduce costs - there's little practical advantage to the user, especially on a tower system that you're not going to leave on the train - if it ends up costing more then either Apple are trousering the savings or they've miscalculated.