That is always a trade-off. Easily removable antennas would make it impossible to pass homologation in some places.
Remember this is how the RP-SMA was invented: WiFi manufacturers wanted to have removable antennas for production and shipping efficiency reasons, but had to do something so users could not connect larger or external antennas. So make a difficult-to-obtain connector. Of course the market will arrange that those connectors will become commonly available.
The problem you’re trying to solve is to design a 4-channel antenna system for the 2.4 GHz Wi-Fi band and a 4-channel antenna system for the 5 GHz Wi-Fi band—without any special knowledge or equipment.
The best solution, since you’ve already purchased this rare device, is to place it on top of the case and use the built-in antennas. Alternatively, you can disable its Wi-Fi and use it as a regular switch, while using a separate device for Wi-Fi.
Although you didn’t specify the area you need to cover, if it’s 10 square meters, you can do whatever you want.
For the exhibition, it’s best to buy an enterprise-grade Wi-Fi device, such as a used Ruckus. SOHO-grade Wi-Fi devices don’t work well in crowded areas.
One can always rent one of these for a mere 
US$ 1,200/day:
https://popup-wifi.com/products-pricing/the-workhorse/
For events dedicated to people that are into burying gold coins to grow money trees they seem appropriate. 
We are Mikrotik junkies
Be practical about this.
Have been using Ruckus where I can since ... I do not remeber. Do not know what WiFi glitches mean. Had CAPSMAN installations but it was a pain comparing to Unleash self configuring, self healing network.
Used WiFi 5 devices you can find for a dozen bucks. Worth trying even if you to decide trash them out.
I spent quite some time trying to find a practical solution.
What I came up with is directly attaching four stub antennas and routing out the other four through the holes left after removing the stock antennas. Used some cable glands that almost fit. I used a stepped drill bit to slightly enlarge the holes. The connectors can then be rack mounted.
I could have left two of the stock antennas in place. But they are just a little to long and tend to be in the way.
Nice job - thanks for the picture!
I do that too, just flashed bunch of UniFi APs with Openwrt last week to use them for guest WiFi, along with Mikrotik and CapAXs and capsman.
Maybe it would have been slightly better to put a 2GHz and a 5GHz antenna at each of the pairs of SMA connector places, instead of 2 antennas for the same band alongside.
(i.e. swap 2 of the pigtails to internal connections and swap 2 antennas)
By the way, I’ve seen warning labels on various wireless devices not to operate them without connecting antennas first. Could someone explain why?
Yes, I’ve wired them in 2.4+5G pairs already. The small antennas are just for testing the fit. I might end up using those standard universal antennas for all four. I might also add a third of those dual band panel antennas.
Because a significant amount of power will be reflected from the open end of the high-frequency line, which could damage the transmitter.
