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.