I think you’re going off the wrong angle here, @Henry_Bruns.
First of all, the CPU does matter. First of all, even the latest GL-AR750S uses a QCA9531, which has its own limitations (e.g. it doesn’t support DDR4 RAM, and I highly doubt the WiFi 6 throughput would be great). Qualcomm does have dedicated SoCs for WiFi6 applications, even ones that support DDR4: for example, the Networking Pro 1610 Platform, which, based on the specs, would be the perfect candidate for the next line of high-end routers, with the travel routers getting probably the lower end of this spectrum (say, the 610 or 810).
Also don’t forget that WiFi 6 will require at least 3 antennas (but rather, 6, to provide 2x2 MU-MIMO and be able to act as a repeater without major setbacks), which will increase power draw and heat as well.
For flash, 16MB SPI NOR flash is perfect. You don’t want to go bigger, as NOR flash is expensive (but secure, no sudden bad erase blocks). Then you can pair that with a larger NAND flash (like the MUDI does), and make the OverlayFS of OpenWRT out of that (read-only kernel and root file system reside in NOR flash, user configuration, including installed packages, reside in NAND).
For LAN, I’d go with 3x 1Gbps ports - 2.5Gbps is still quite expensive, and not a lot of uplink routers support it. Especially not while travelling, you’re lucky to get 50Mbps in a hotel, let alone 1Gbps; making 2.5Gbps a bit useless for a travel router.
For Wifi… you’re looking at a RECEIVER card. That’s why it’s so cheap. The 200AX (and its brothers) are fine for a device that is receiving a single connection from a router uplink, but is terrible for any sort of access point usage. You’ll get some massive issues the moment you have more than 3 devices connected to it. Consumer grade wireless cards meant for clients are NOT good substitutions for this type of hardware.
I agree on the WWAN card, however it adds further complexity and possible incompatibility issues. Because of that, I’d rather see more USB ports on the device (say, two USB-A 3.0/3.1/3.2, alongside with a USB-C power port similar to the MUDI, but also allowing proper USB connection over it). Maybe even a recessed USB port behind a door, so that a 3G/4G dongle can be plugged in and hidden without it sticking out?
Overall, designing a new router is not as easy as slapping together a list of wants. It will take time and effort, and if you really want all those features, well, it will cost.