That is the ultimate fear, and de-restricting the AR may in fact unintentionally trigger such an event.
Let me explain my train of thought, ya'll tell me if my logic is flawed at some point as I have given the subject considerable thought.
AR's basically come in 3 distinct flavors.
Factory made, complete rifles with an original barrel lenght that, would it not be for the OIC which deems them restricted, would be non restricted. I will refer to these further by "category A" or cat A for short.
Factory made, complete rifles with an original barrel lenght which would remain restricted regardless based on barrel lenght. Cat B
And home-built jobs assembled from a lower in various state of completion. Cat C
AR owners generally own a single lower of their liking, and various uppers to suit their taste of the day(many of them anyway).
When it comes to Cat A rifles, well if you own a Cat B upper (or God forbid a Cat C upper whose barreled you at some point chopped off), once the Minister signs off on an OIC which removes the AR-15 design from the "deemed restricted" list, that upper is now either an expensive paperweight similar to 12(2) thru 12(5) rifles, or a prohibited weapon, since the very second that you dare push in that front pin to put it on your "non-restricted" lower, you have now created a prohibited weapon and made yourself a criminal.
Cat B owners would be largely untouched since existing regs would still apply and you can do pretty much whatever the hell you want barrel-wise with a restricted firearm. Your AR would still be confined to the range only however.
Cat C is where it gets interesting, and scary. Those fine folks would most-likely fall into the "home-built firearm" regs, which stipulate that it must be submitted to the RCMP for "evaluation". Now say the RCMP would put in place an internal "policy" that they won't "evaluate" more than one "home-built-firearm" a year, something that is well within their power in the existing law, and you won't ever see your precious firearm again.
Then there's this whole business of people whom have made it a habit of installing all sort of parts inside their S/A AR's which were intended to be used in F/A firearms .... Given the fact that the RCMP has made it a habit of tinkering with "new" S/A firearms (using a full team of engineers, master gunsmiths, and a ridiculously-well equipped machine shop no less) until they can get a firearm to fire twice with a single pull of the trigger just so they can "reject" and seize it and well, you get the idea.
I cite as an example a firearm known as the M96, which is no longer manufactured but opened a hellova can of worm merely a few years ago when it was available with uppers (the thing used a two-pin upper/lower system quite similar to the AR, but the internals were quite different) of both restricted and non-restricted barrel lenghts.
Since the CFC/RCMP won't (not like they can't while staying within the law) issue multiple registration certificates for the same firearm ... You get the idea.
You know what, enjoy your AR while you can and when the cops come knocking, give them your rifle and cry.
I do not see the ARs being unrestricted ever, in fact I expect a huge "let's collect them all" party (i.e. confiscation) in my life time...
Addition: I do send out letters, contribute to CSSA/NFA, talk about issues and encourage fellow shooters at the range to join the fight.