@BKKR there is no reason that it would not work, but we are still awaiting our 916x APs that we ordered...
You could disable the 6GHz band if the models with external antennas are WiFi 6 only, as that would be the only potential issue I can think of.
We are going to mix them with WiFi5 models in the same room and aim to leave all WiFi6 and 6E features enabled, only downgrading if we see issues.
I'll let you know once we get them!