I'm kind of going that direction to be honest. On a base level I'll only actually have a couple of ARs in each category as it were; few AEGs, 3 TM SOCOMs and 1 GBBr (for now).
I get that people who don't have the time to intricately research the many, many kinds of handguards etc just see "yet another M4'". But especially once you get in to the world of GBBRs and fitting real parts to them, then (IMHO) the mind-blowing amount of parts available to fit means that classifying it as just one type of firearm is pretty much incorrect. Especially when most airsoft guns do the same thing on the insides.
There's also the serious aspects of ancillaries, accessories, LBE and tooling. I mean sure you can buy an MP5 and then a suitable battery a scope mount and a box of plastic mid-caps won't cost all that much in the grand scheme of airsoft. But when you've dropped everything you've got in to the very best magazines for your one type of gun, the greatest mag pouches money can buy, expensive accessories that often might not suit another platform and (most importantly) invested significant time in to learning intimately how to work on one platform and then money in to buying very specific tools for that one family of guns... well you kinda wanna stick to your strengths, as it were.
Obviously a lot of airsofters out there want a gun wall with as many different models as they can physically get because that's what they think is cool, more power to them. But I joined up as an armourer because I like working on guns and airsoft lets me do that in my spare time using exactly the guns and parts I personally like the most, rather than the ones a military publication says I have to use (which are probably quite boring a lot of the time). Not having an argument here with you in any way or saying you're wrong, just putting across my view point for those who might not have considered some of the points above.