Would A Rifle Job Ever Be Possible?

[Zojha]

MCH on its own is a fun job to play.

That is subjective. Objectively, you can only measure whether something is "fun" or not by looking at how popular it is relative to its power (or more generally, relative to its reward, because the principle applies to content as well). If something is unpopular in spite of being powerful (or having lots of rewards), chances are it's not very fun. On the flipside, if something is popular in spite of not being powerful, it's safe to say it's fairly fun. And if something is popular and powerful, or unpopular and weak, it's not possible to tell whether the effect is caused by the power or the enjoyability.

As for musketeers or rifle jobs in general, I feel that MCH is pretty much intended to cover that. The guns tend to be on the longer side and the new sprint animation is specifically meant for longer guns (it looks VERY awkward with the Makai Mortar or even the gunblade series). I doubt they'd make a new one.