Just for completion:
… really sad that Banana Pi and ASIARF didn’t agree on a common interface 
- Maybe for Wi-Fi 8?
And I found another reason why Banana Pi should add a shield to your Wi-Fi cards:
→ They could stamp their logo on it! 
To complete the topic:
The AsiaRF BE14000 is now available:
It looks like GL.iNet has an attractive upcoming router with Flint 4, offering BE14000 capabilities too. 
Hopefully Banana Pi and GL.iNet can talk to each other about common, mechanically compatible Wi-Fi 8 modules. 
I see that this module from asiaRF is not physically compatible with the bpi-r4.
Yes, to run this in a BPI-R4, you would need something like this:
https://de.aliexpress.com/item/1005004984753432.html
But you can only use 2× PCIe 1-lane, which could may be enough?
It looks like external power could be supplied to the adapter.
But… I don’t think it’s worth the work! Waiting for the next BPI-BE14 version may be the better option.
I decided to go with the AW7990 (…but I haven’t turned it on yet.).
I’d really like to get the new version of the be14, one that completely fixes the issues with its predecessor, but there’s no news about its release. So, I’m increasingly inclined to sell or throw away the bpi-r4 with the be14 and buy a regular router from a reputable manufacturer whose Wi-Fi WILL work.