Financially, it wouldn't be a good move for 343 - they need people playing Warzone.
Why would you stop playing Warzone? You don't stop playing Team Slayer because someone created the Infection gametype no?
Yeah, seems that way. SWAT is a thing, tho, so it's clearly possible, just not visible atm.
And it's pretty clear that the reason they don't allow them in Customs (and eventually Forge) is so that people have to get them through the REQ system. If you can play with Whiplash to your heart's content, why grind out packs for it? Allowing unique models is a good compromise, IMO.
You just handicap the development of the community though. Things like grifball, infection grew out of fan creation. You don't want 343 hand holding everything. Let's things be organic. I'm just saying we could've seen some unique stuff come out of custom gametypes developed if we were given full use of these req's. Maybe next game. I'm still happy, but just saying, it's 'always the next game' where you can really get something you really want.