Maybe have them receive bonuses for playing together, for example 5 players IG regular guards on the field, if they remain close to each other and are in a squad they get bonus armour/offence the more that gather close to each other until a certain max limit has been reached.

Yeah, technically it hard to realize, but developers going to use so-called famous PikkoServer technology with 1000 players on 1 server. So... I suppose, it can be.

Well I can see the idea of 100s of dudes with laser pointers and T shirts fine to be F2p, there has to be a choice other than Orks. For starters as it would actually do more harm than good with Orks being the only choice.

The other thing we have to do as a community is for in order the game to actually function in a way that keeps most of us and the Devs happy, Is to allow the lore to be flexedor glazed over enough for it to function In a game and maintain some sort of balance, but still keep most of the feel and immersion intact. but what I bet we will see. is when something is implemented in game for balance such as, a skilled guard player going mano a mano with a marine and able to hold his own for a while. only to have the marine player whine and carry one spouting its not like that in the mini game or the movie marine novels I've read etc.

Finally not every guard unit is as disciplined and obedient, follows structure or obeys the High lords fully.
there are plenty of guard units some green conscripts, others are elite storm trooper. there is potential for many more just have to think outside the battle bunker a bit

Don't forget Imperial Guard get a lot of kick-ass fire support and vehicles too. It won't matter if your one IG can't go toe-to-toe with a space marine if there's a bunch of Leman Russ tanks blowing the crap out of huge chunks of the opposition in addition to airstrikes and artillery. There could be other ways of effectively simulating the Imperial Guard tactics like applying % based damage increases on targets hit by lasguns. So if five guardsmen are shooting at a space marine, they all apply a 5% lasgun weakness so their focussed fire is doing a lot more damage.

The Tanks Vs. Robots-test proved you could have 1000 players in a single battle. The server might be ble to handle more
The thing is that I really don't want this idea to be implented. For every potential squad (1 player) of Imperial Guards the server might be able to handle 2 less "normal" players, and thus it is in my book not something that should be in the game.
This is of course just speculative from my part and might not be the case. Would love to get a word from a developer.