I find that my views are moderating on this issue, too.
I certainly discount temporary Aspects/Maneuvers/Consequences/temporary Powers as sufficient to invalidate the Pure Mortal bonus. Points to that side for using that tactic to try to bring the opposition closer to center, though - it reminded me of the scene in the "I, Robot" story, when the robot's legal team put out a campaign to have it made law that any prosthetics or artificial organs would render their bearers robots, and therefore no longer human, which of course tilted the argument back towards "where is the line?" rather than "dirty robots shouldn't have rights!"
I also feel that several of the Templates just aren't appropriate territory after someone starts as a Pure Mortal. I just don't.
White Court Virgins *are* the proto-form of the White Court Vampire - not Pure Mortal. Even if the Virgin was raised outside of the White Court (adopted, abandoned, secretly fostered for later political reasons), that just means there is a Virgin out there with White Court Virgin powers, but less chance of knowing his heritage (or maybe more, especially if he was stolen away by a Vampire Hunter to train as an ally). But the player still knows what he opted to play, and choosing White Court Virgin means one is either planning to go full White Court later, or explore the possibility of breaking the cycle and joining the ranks of Pure Mortals later, in-game.
I think Changelings (and by extension, Scions) *are* the gray area in this discussion, and no other template. It's not very gray, mind you - it is almost guaranteed that they are going to not qualify as Pure Mortal - but hypothetically, I can see someone opting to take no powers, and leave The Choice as a purely philosophical one, with no experience using Fairy powers.
But governing all of this is intent. If an Aspect with an intrinsic supernatural theme is going to (by intent and design) skirt a Supernatural Power (in the way I laid out however many pages ago), I think that the player needs an appropriate Power to go with it, and if not, they need to sacrifice that Pure Mortal bonus voluntarily.
If that Aspect with an intrinsic supernatural theme is a placeholder for later supernatural stuff, but the player is fine with keeping it to mundane Invokes for the time being (though Compels can still be of any type, mundane or supernatural), I would consider retaining Pure Mortal until such time as the player puts into action whatever Supernatural plan is in mind.
And if an Aspect is clearly supernatural in nature, but the implication is that the weirdness is happening TO the character (extrinsic) rather than under the character's control (Favored Singer of the Summer Court; Family Debt to Odin), and/or that weirdness is facilitated by a PC or NPC proxy (My Wizard Buddy; Pet Troll; Followed by the Butterfly of Chaos), then I think Pure Mortal is preserved.