The Hospitallers still exist.

There are about 40 "First Class" members, 600 "Second Class" members (mainly titled "Knights in Obedience") and 12,400 "Third Class" members.
(per Wikipedia, fwiw)

This is a very-interesting notion.

I don't think Jim's going to write it this way; but it's very interesting!

The pieces hang together well-enough for me to now think it's likely that "replace Lara's Hunger-Demon with a Wintermantle" may very-well be part of Mab's planning (if only 2nd or 3rd tier contingency).

I've intentionally not specified the Queen-Mantle... Lara of course hardly qualifies as "virginal" but maybe the magic can admit of a "from now on" definition.  It'd be incredibly-ironic for "Queen of the Sex Vampires" to become mythically-virginal!      And we know (from the disastrous Carlos/Molly event) that Jim's very willing to torment other characters than Harry, with this sort of thing.  And it'd give Molly an "out" from the Ladymantle, if Harry could find a way to initiate the transfer without killing the current owner...

Or, just do the "normal" Queen dies + Lady-becomes-Queen + Ladymantle-needs-host sequence, with the Winterknight's fiance close to hand.  Ratchet the Molly/Harry tension another notch, I'm sure Jim would like it for that if nothing else.

Or just some direct Lara-gets-Queenmantle path.  That might eliminate the "marriage" elements, though, if there's any incompatibilities between the mythic Winterlaw ideal of "marriage" and the Queen/Knight relationship.  I think Jim's more-likely to write the complex one that loops-in Molly, ratchets-up tension, and tweaks Lara's twerk.

So, lots of elements come together very nicely indeed!  I like your theory a lot, @Avernite!

I think the words "close to Lara" are meant to make us think it means when Justine started to work for Lara.
But in my theory it can also mean "close to Lara" in location. Meaning either Justine got infected during her imprisonment in Grave Peril and because she was Thomas' girlfriend and Thomas during that time often met with Lara offscreen. So she often was in proximity to Lara.

Or Justine was even the first vector, the first nemfected person.
Iirc the question in Battle Ground was "since when have you been in Justine?"
What if Justine was Nemesis' plant all along. Everything planned, from the moment she met Thomas till the end in BG. Becoming Thomas' girlfriend could also be seen as "close to Lara".
I always thought it weird, that the Reds wanted her before. What interest  could they have in one weak human girl? They could have any other girl. Why Justine?
And yes, all of this already implies that in theory the Reds worked for the Outsiders.

All of this almost purely speculation, of course.
 
Edit: the Reds' interest could have been faked to push Thomas to act and safe her, thus making it more probable for her to become his girlfriend.

This is interesting. If Lea hasn't been 'cured' but treated, then it could be that nemesis in some capacity remains with her or with Mab/Winter's Heart.  That split of power is a significantly higher investment than likely those of mere mortals.  It could be that like others said that power in stasis has led to a weakening of Nemesis' power that can be utilized outside of that stasis.