Details about the NUC 12 Extreme have leaked, Intel's next flagship mini-PC. The NUC 12 Extreme will include a PCIe x16 Gen 5 slot for next-gen graphics cards, and dual-slot ones to boot. The NUC 12 Extreme will be upgradeable, but it may also be rather expensive.
https://www.notebookcheck.net/Intel-NUC-12-Extreme-Specifications-and-suspected-prices-of-Alder-Lake-powered-mini-PCs-leak.602191.0.html