There are so many logical fallacies in this argument. I get the preference for having a traditional tower that you can store everything internally, but argueing that having an updated Mac Pro is going to be cheaper than an iMac Pro in the long run is way off base. For all components you’ve listed there isn’t a single one besides possibly the display that makes very much sense.
- Keyboard/Mouse - the iMac Pro’s slate gray keyboard, mouse and track-pad are already in such high demand you could easily buy an iMac Pro and resale the keyboard, mouse and trackpad at substantial profit. I’m almost certain these could easily be resold on eBay after purchase for $75 for the mouse, $100-$150 for the keyboard, and $150-$200 for the trackpad. When the iMac Pro was first shown, those are things that many got excited about.
- Display - you said yourself you’d likely get a new display eventually for the Mac Pro. Why not just keep your current display and use it with the iMac Pro. Most people that work seriously on their computers that I know of find a single display cumbersome even when it is is a nice as the 5K display in the iMac.
- Storage Components - TB3/USBC enclosure are cheap. For the money you’d get from selling the mouse/keyboard/trackpad you could easily buy a nice 4-6 bay TB3 enclosure.
Ultimately I think you are hoping for Mac Pro that is not going to be anything like what Apple will provide. Apple has already shown they are completely on board with Thunderbolt for expansion. They’ve also said that the new Mac Pro is going to be for the most demanding workloads. I see one of two scenarios for the new Mac Pro and neither one of them will fit with what your describe.
- Apple releases a new Mac Pro that looks a lot more like the trash can Mac Pro than the cheese grater one. It will continue to use TB expansion for everything except RAM, NVMe slots, and possibly a GPU. I highly doubt the new Mac Pro will have any SATA or SAS port internally, those are legacy interfaces now that would have died off 5 years ago if intel/Apple and even Dell and HP had their way.
- The new Mac Pro will likely be based on a dual or quad socket Xeon design, and the price will likely start at $7500+ without the keyboard mouse or display. That is the type of computer they mean when they say it will be designed for the most demanding workloads.
I also wouldn’t be suprised if Apple pushes really hard into the eGPU realm with an update to TB4, and support for their own eGPU enclosure, something that would benefit all their pro machines (MBP, iMac Pro, and a new Mac Pro). Just my 2 cents.
I'm going to number the points 1-3.
1. Keyboard and mouse can indeed be resold, and I would indeed do that in a heartbeat, however buying the iMac Pro in the first place requires considerable capital. I cannot rely on being able to sell what I have after the fact. The money flow is larger than what I have available, simply because I haven't been in my job for very long and recently came out of education. And frankly, it's ridiculous that I should even have to go through all of that.
2. This counterargument makes no sense. The problem is not the number of displays, but rather the cost that this display adds to the price of the computer. I cannot afford the computer and the display simultaneously - they add up to too much. Also, call me crazy, but I actually don't like multiple displays. I have 2 displays, and one of them is almost permanently disconnected and turned off. I prefer virtual desktops.
3. I don't have that money. This point collides with point 1 directly. Maybe I can afford it if I don't have to buy the screen simultaneously. I could also buy it on financing, but the costs are just too great.
I agree entirely with Apple on how they are handling expansion, but GPU's, CPU's, and RAM cannot be upgraded via TB3 or even TB4. You require more bandwidth. This is indeed the case with the Mac Pro 2013. Apple hyped its expansion capabilities up and said we don't need to make it modular internally, because you can expand it externally, but for these 3 very important components this just doesn't work.
As for your suggestions about what Apple will release, I think you're wrong on both fronts. I don't think Apple will make another trashcan or trashcan-like computer. Most of them broke due to poor cooling, it was a colossal failure, it didn't take off in the PC market, everyone laughed at it, and it just didn't really work and wasn't supported well on the Mac platform, and they don't want to design themselves into a thermal corner again. I put the chance of another trashcan at virtually 0. It ain't happening.
I do think you're right that the Mac Pro could sport dual or quad socket Xeon boards, but I am very certain that there will be a config costing less than $7500. If Apple wants to sell that product at all, they just cannot make it that expensive. When they say "most demanding workloads" I really don't expect any more than the iMac Pro, which was also designed for the "most demanding workloads", and then it can go up from there and go complete nuts, sure, but there will be a cheap, relatively speaking, base config. They're not gonna start at $7500, that's utterly insane.