One thing I liked about the series is the lack of bullshit unlocks that made the game unbalanced. Everyone used to play on an equal playing field.
I'd bet my house and my car that there will be a playlist/gametype, with a substantial multiplayer population - that will be vanilla, no perks, fast, BR gameplay.
I'd bet a small fortune that if anyone can make a perk system 'fit' into Halo's MP gameplay, it will be Frankie's 343 Team. Personally, my initial thoughts on a perk system lead me to believe we will see something extremely mild in comparison to COD/Battlefield. Possibly something similar to League of Legends Runes. Whereby Spartan customization may net you tiny/incremental stat increases in the form of sprint/ability cooldowns, reload times, jump height, health/shield regen etc - obviously in lieu of other potential stat increases. That is of course, purely speculation - but I'm 99.9% certain that we're not going to be seeing Sleight of Hand/Stalker/Cold-Blooded/Danger-Close, game changers.
People want customization and perks - it's going to be a critical aspect of the Multiplayer to implement - if the game is ever going to grow and maintain a larger ongoing player base - let alone get anywhere near COD numbers. People want to be able to select a bullshit perk that artificially compensates for their play style or gives a possible unfair advantage over an enemy - the trick for 343i, will be hooking these players, without going full-retard (COD). There is almost definitely some sweet spot between perks/customization, and vanilla Halo/arena-shooting, that will please a significant portion of the userbase (and keep Halo fresh for a while). For the more traditional MP fans, the straight up BR, no-perk playlist is going to be plenty.