I also agree with all of @Sven’s points, with a few of my own:
Laptop
- The internal keyboard and trackpad must be on its own bus
- all other internal peripherals should either be on their own dedicated bus, or at the very least grouped by function/purpose
- integrated graphics AND discrete GPU (possibly multiple GPUs, for passthrough fir gaming, video editing and mining)
- Multiple M.2 slots for SSDs
- MANY MANY SODIMM slots for RAM for Qubes
- Kill-switches for camera
- Ports ports and more ports, of all varieties (maybe even interchangeable like the Framework Laptop, allowing more flexibility to port passthrough)
- Maybe some kind of “USB Condom” on all USB ports
- FOSS-friendly Ethernet (potentially multiple RJ45 ports) and wifi (preferably multiple antennas, for pentesting)
- Enough battery life for 3-4 hours of use at full load
- 4k display (potentially touchscreen)
- Rugged enough to “take a beating”, but elegant enough to not look like you’re on an archaeological excavation endeavour
I don’t care if it’s a brick, I’ll still carry it round 
Desktop
- LOTS of PCI slots
- LOTS of separate USB Buses (preferably max two ports per bus, as you can always use adapters to connect more devices)
- Maybe some kind of “USB Condom” on all USB ports
- FOSS-friendly Ethernet and wifi
- FOSS BIOS (ideally Heads or a fork of Heads)
- UPS (just in case, even if it’s only a 10-minute battery, just so your machine can shut down properly)
- SILENT FANS, or no fans at all! (I’ve done my time in a server room)
Am I missing anything?
Disclaimer: This is a wishlist, and I’m fully aware that all of this in a single machine would be difficult, if not impossible….