I'd say that if you want this weapon to primarily be considered as a supplement to the Medic's MP7M, you need something that:
a.) Is more effective than the MP7M in terms of damage-per-shot.
-and-
b.) Weighs less than the less costly, off-perk weapons a Medic might currently use. (At least early in the game.) In other words, weigh less than the 6-block LAR, Bullpup or 8-block pump shotgun.
It could be argued, I feel quite successfully, that the 4-block MAC-10 and/or dual HC choices fill this niche. Some might also advance the notion that if you provide a weapon that is clearly more effective than the MP7M, the Medic's primary role could be threatened. Methinks that depends on the individual, not the available weaponry.
If you accept these parameters, and, of course, no one is under any obligation to do so, I'd also say that you have a fairly daunting task ahead of you. It should be a weapon that brings something to the party unique, and apart from, the MAC-10 and HC, and weighs no more than 5 blocks, at the very most. And, should be relatively inexpensive to buy and feed, too.
I'm struggling to think of something that would fit within this criteria. Off the top of my head, the only thing I can conjure up is the M1A1 .30 Carbine, the paratrooper variant with the folding stock. This is a plausible 5-block weapon, semi-automatic, with a decent sight-picture. It would be inexpensive, have a damage-per-shot of about 42-ish, good accuracy and LOW recoil.
Note that I'm *not* advocating this weapon, but simply trying to approach RedShocktrooper's belief that there is a need for additional Medic weaponry by defining a requirement first, and then seeking a possible answer. While I see no harm, and certainly some enjoyment, in brainstorming, (especially in the "Ideas and Suggestions" Forum), I have no real expectation this will lead to anything. Would that it were so...