Hey @Dugdog47 I've been asked about this before by friends so have thought about it a bit too.
Long story short I think the best way to go about this would be to have all the quads GPS controlled actually because without the known position for all the quads they are going to be likely to drift into each other or off into the field I think over time assuming you're just sending the same control input to all of them and letting them do their own thing.
Pretty sure the way intel and the like put on those 100s of quads flying together thing works is there's a central computer that has a virtual version of all the quads (just points in space) and it does some translation to turn those virtual points into GPS coordinates (basically translate from virtual space into real space near the take off location or place for an event). Then the master control computer will send out all the GPS coordinates to each quad to get them to move "together" or coordinated but there's no real manual control in any of that.
Regarding just like hacking it to go straight from manual control input to quads, you could use the rf-nano (this is an arduino nano+rf chip on one board). The RF chip is from a company called Nordic and they basically have their own proprietary protocols for the transmission of data but I believe they can support "multicast" where there is one transmitter and multiple receivers:
I made my electric skateboard controller out of some boards hacked together but end up being same thing as rf-nano (don't think it existed when I made mine but i followed some instructables on hooking up nrf24 chip to arduino and built from there)
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^^ this is my thing (my name is Shaun in case curious but @wafflejock is totally good too )
So yah to sum up, would say yes sort of possible in a couple of different ways, my receiver code for the controller above is just using a single channel basically and PWM pulses to send to an ESC that controls motor on my electric skate so would have to look into arduino libraries that do sbus or some other protocol where can send multiple channels on one line (ideally), otherwise arduino usually has at least a handful of PWM capable pins so can feed into FC that way.
oh also also, my day job I've been working on IoT things for like 6 months and turns out a lot of those things can use STM32F4 or similar chips at the core of them (usually with some supporting wifi hardware) so another way to go is use AWS IoT platform add all your quads to a greengrass group and somehow get them acting as MQTT clients through a single broker to exchange messages I've gone too deep