While I get that every rogue spec will have people come out and say "no, not this one thanks"- and importantly, based on kit, you'd expect combat to go ranged before mutilate, and sub never ever- I think the idea is pretty good.
Also keep in mind: They just dropped this bomb on hunters. First they were like "ANNOUNCING THE HUNTER ARTIFACT MELEE WEAPON" and then a couple days later were like "also-ur-spec-is-now-melee-kthx". Blizzard has ALWAYS considered the hunter specs more generic than the rogue specs, and probably kicked themselves for not locking each type of hunter to a specific type of ranged weapon. But still, if you've been a survival hunter since beta, you either love this change, or hate this change- and that's true if you've been a survival hunter since last week, too.
So with their ability to just up and change everything, yes it is possible that they will do this to rogues. If combat used daggers on live, they might have actually done it already. It's definitely strange to consider that hunters could be taking your melee spot just with an on-the-fly respec, while also being totally valid ranged in all the same armor, jewelry, and trinkets. That's a ramp up in pure power, but it's not a ramp up being enjoyed by any pures except hunters. It is very strange for hunters to get a melee spec and rogues NOT to get a ranged spec... but that seems to be the plan at the moment.
Anyway, it wouldn't be mutilate. Back in the day before mutilate, when assassination had a niche of "better finishers, now go away kid", you could make that argument. When you'd dip the spec for cold blood, you could make that argument. When you'd spam hunger for blood or lose all your everything, that was not a great spec. But once it became mutilate for reals, it had a pacing and kit all its own, and it had its own damage type as well, with strengths and weaknesses. I don't think we'd see assassination go anywhere.
They've always had an easier time coming up with stuff for melee. They just think of a move that involves your character, and your weapon. Whereas all the ranged moves normally just involve your weapon, and the few times they involve the character it's a buff or a color or whatever, it's not killing spree.
Anyway, yes, they should (but not mutilate), and no, they probably won't.