Lindsey Stirling is simply amazing, awesome, and a sheer joy. I want to see her in concert someday. Maybe after I move somewhere that people actually go to.
Anybody else pick up a pretty cool "Luke, I am your father!" vibe here?
Just you, me and the card sharks 
Don't forget to mention the shades of Phoenix 1.0 with the mirror and the shack. Poor Viscaria. She wants so badly to believe in the world, she's been given so little reason to do so.
Take player's paranoia. Use it against them. Rinse and repeat.
I'm in training the next two weeks so posting will be sporadic.
When you have question about the rules as written, it doesn't get more definitive than this. (So much for "It's raw, now stfu before I shut the game down!") 
Line editor fiat is line editor fiat.
Read your quote, thought about it, read your reply, laughed.
No, no, no! They've got it all wrong. That doesn't prove women wore bras in the middle ages, it proves the existence of Time Travel!
It has been suggested by third parties that, given the existence of Vin Diesel as a shield grog, we also need Jason Statham somewhere amongst our people.
I say we make him the new linguist.
After all this time as editor he knows how to end a potentially endless Magic theory argument, I'll give him that.
It really doesn't. Some rationale behind a statement, even if it doesn't work with the game mechanics is preferable than a simple statement of "No." I could continue to mince words. 
So I shall!
I like the reasons that Parma doesn't get knocked down when going into a foreign Aegis, I can agree with them. Don't get me wrong. Again, it's a moot point for this saga, but if one spell can knock down parma, it's not much of a stretch to see Aegis can knock it down...
Tangent: What would the MuVi spell be that would increase the Penetration of a spell cast by a friend?
Wizard's Communion...
I don't have a major problem with Winds of Mundane Silence dispelling Parma Magica, per se, since it was designed to cancel any and all magic in the room, if the spell is powerful enough. But it only seems to affect "active" magic, spells, what not. I would like some clarification, though, on whether it affects all or some supernatural abilities. For example, if there's a werewolf or a skinchanger in the room when you cast the spell, is it forced into its natural form? My gut reaction would be yes, because they are ongoing magical effects, and it could be argued that since they don't have an Ability or Art, they have no Resistance and thus WoMS automatically penetrates. But I'm not 100% comfortable with it, though.
I have a rule in my games, though it does have some flexibility, where one ability doesn't typically get to mimic a power/effect that requires a different ability. So for example, there are some spells designed to target witches, hedgies and shapeshifters that specifically turns off their shapeshifting, I think they're listed with the Pralix tradition. Since there's an actual spell that does this specific feat of magic, I'd be a little reluctant to allow such a general spell of WoMS to have the same effect. Basically use the right tool for the right job. Now then, having said that, the WoMS should be able to cancel active magic, but in this case is stepping into another spell's territory it might require more power (higher level and/or Penetration), basically it accomplishes what another spell can do just by virtue of more power. The spell designed to knock out the shapeshifter power might be easier to cast, whereas the WoMS can have the effect but only if you really push it.
Just my opinion.
Winds of Mundane Silence knock out supernatural abilities? That is very interesting.
Think extremely carefully about what your asking for. If an AC is convenient for the PCs, it will be just as convenient for NPCs.
IMO, the duration of such a letter is in days, as in less than a week, and is probably held for the duration before given to the Redcap for delivery, destroying any utility for use as an AC.
I might even argue Hours duration once it leaves the location.