we'll never know until it happens, It's a probability, because EVERYONE is asking for it- but every single element of the game effects balance, I mean - someone having a silencer and a Red Dot isn't very balanced, because the limitation to ironsights if you want to stay "invisible," whereas with the red dot, you have a better chance of hitting the enemy, but are not always "invisible," and with the ACOG you zoom in x2 (I think), but the sway decreases accuracy.
Hence, every single thing in the game has a counter effect, and allowing multiple attachments would ruin the game for newer gamers. It'd be hotter anyways to have multiple perks.