It would be great to have a good secondary wifi card for penetration testing or doing some other interesting things (like a permanent AP for raspberry pis to connect to for SSH).
Some ideas for specifications:
- Switchable between an external antenna via SMA connection and antenna on PCB trace (see note A below). Maybe even a directional antenna. Open to ideas from others about improving range beyond the internal antenna.
- USB 2.0 interface may not be suitable for faster data rates but it has the simplest connection via the USB-c connector see (note B below)
- a good driver that allows Promiscuous mode on Linux (See note C)
Note A
This is a PCB trace antenna for 868-915mhz but maybe they could lend their expertise. Not sure if a PCB trace antenna is even a good idea for this presumably it would just be shorter since it wifi is 2.4 or 5 Ghz. I believe they publish their design files on github for this.
Note B
Looks like the Wikipedia (ref below) claims the newest wifi [IEEE 802.11ax (aka Wi-Fi 6)] goes up to 11 Gbit/s 
USB 2.0 (simplest for circuit design) is only 480 Mbit/s. This speed would be almost fast enough for IEEE 802.11n (aka Wi-Fi 4) at 600 Mbit/s.
All this info from here: List of interface bit rates - Wikipedia
Note C
Looks like a good USB dongle that is known to work for this application is the Alfa AWUS036ACM (faq [Aircrack-ng]) but I’m not sure of the chip set. Could be a good starting point.
Generally, I would identify the chipset via the method here until I found a chipset I could find on digikey or mouser and go with that.
Digikey publishes KiCad libraries for some of their parts but I don’t think its comprehensive.
Looks like mouser does the same but they claim its their designs are compatible with many different ECAD software.
That’s all the thoughts I had for now. Just wanted to get that first bit of research out there. I am a busy grad student so I probably won’t have much time to check this but I can give advice if I have the time.