In fact, you can get the new entry-level Mac mini plus the Sonnet Breakaway Puck RX 560 [0] for US$1100, now that the eGPU has dropped in price to $300. Whether any given person would be satisfied with that configuration is, of course, open to debate.
While this is probably too niche to make economic sense as a product, this seems like a perfect use case for a vertically-mounted PCIe slot, creating a tall GPU pedestal for the Mini in a similar vein to the G4 Cube.
It's the only non-Pro designated Mac that has four Thunderbolt 3 ports. I don't think you'd find this level of I/O in any other machine in this price range.
That incredibly powerful I/O makes for tons of expansion possibilities. Storage, GPU, etc.
Not all Thunderbolt 3 ports are the same. Good chance that two ports are sharing a single PCIe 3.0 4x controller. Since PCIe 3.0 is good for ~7.8Gb/sec/lane, you're looking at two 40Gb/sec Thunderbolt ports sharing about 31Gb/sec of bandwidth on the PCIe bus. Okay, probably not that big of a deal really.
The point being that a "Pro" system might have 4 individual Thunderbolt controllers, each getting their own 4x PCIe 3.0 lanes.
I think that's why the specs say "Up to 40GB/sec" on the page. It sadly doesn't say which controller it has... But I guess my whole point is really moot in practicality. Good luck saturating that much bandwidth.
Mac mini, iMac Pro, and Macbook Pro all have two Thunderbolt 3 controllers.
The Mac Pro starts with two controllers but can be configured up to six.
The I/O is actually pretty good and provides for a ton of headroom for expansion down the line (I'm thinking primarily storage and GPU for my use-case).
I can see a pretty high powered eGPU saturating the lanes.
I don't think that's the point: if you can ship 16" MacBook Pros with dedicated GPU you could do the same with MacMini; why don't you give me such option? ("you" stands for "Apple" here btw)
desktop grade cpus and gpus have very different thermal characteristics. it quite impossible to have silent + desktop cpu + desktop gpu + very small space.
[0] https://www.apple.com/shop/product/HMT22ZM/A/sonnet-egfx-bre...