*SNIP*
I don't see a mabari packing a weapon.
Well, it is fantasy. . . 

But let's get serious Hercule:
We have the mabari model, skeleton, and attack animations in the game (charge, biting ETC) already, and it's not as though they have to equip actual weapons. Think: Collars and Kadis of Dragon Age Origins: Collars were equipped in the weapon slot, whereas Kadis was in the armor slot. It's not different now than it was then. Collars would have different damage ratings and stat effects, and kadis would provide the armor rating and appearance changes. There is no change in weapon appearance, unless they REALLY wanted to make different collars that stuck to the mabari skeleton. Elemental enchantment would not appear on the character unlike the strange auras they had in Origins (that was weird yo), and if they did it would come from the collar should they decide to make visible items for those.
It's happened before in the Dragon Age series. . .plus, we're getting a bard with a musical instrument as a weapon: never say never.
. . .really, the only problem I see is finding a niche for them to fill, given the semi-limited state of the Mabari in origins, sans mods. EDIT: They'd have to add one or two new animations no doubt to go along with new active abilities, not to mention adjust current abilities along with some Mabari-made ones (It'd likely have passives like Wolf Mauls the Bear, Scenting Blood, Grisly Mutilation, Cull the Herd, ETC. Perhaps actives like War Cry, a Mabari War Howl as an AoE Panic, that make use of the Mabari's terrorizing presence to human infantry.). It'd work as an AoE Diversion, an evasive 'warrior' type (it'd use a charge animation to knock voer flimsy walls) that darts around enemy lies distracting and grabbing aggro while debuffing and attacking. It'd be the fastest teammate given its nature, but also relatively easy to kill in comparison to the other warriors.
EDIT TWO: *crackles knuckles because it's thought rambling time* I can see examples of some abilities as follows, but as I am no game designer I can hardly give details:
Terrorizing Howl: An AoE similar to War Horn, if not essentially the same in basic usage (only made for the mabari. . .as hilarious as the image of a mabari making horns sounds is.). Perhaps an upgrade that temporarily increases the Mabari's attack and/or movement speed?
Overwhelm: The classic ability from Origins just has to return! This ability lets the Mabari pin down certain types of enemies (Essentially Standard Humanoids, including Spellbinders and mages!), doing massive damage to them, possibly along with a bonus if they are stunned prior. A possible upgrade could be a form of instant Grisly Mutilation: if the target dies while overwhelmed, nearby enemies are Panicked. . .OR, killing an enemy with Overwhelm heals you for 'X' percentage of health?
Bull Rush: . . .No difference from the version we already have, just wanted to mention it. ;P