... I think that it is about harry and molly getting rid of the winter mantels.
I don't think so, no; for several reasons.
1/ Jim has stated that 12M will be several other things -- it'll be Chicago-centric, Harry building bonds & community (very-possibly with little-Maggie elements, e.g. education, friends/playmates, ets... maybe even concerns from Illinois' "Children & Family Services") -- it'll be about Harry's grief & trauma, losing Susan (& everything else he lost in Changes), the psychic assaults over the years, and so on: grieving-Harry, ptsd-Harry, stressed-parent-Harry, etc... it'll be about Harry/Lara and the WinterKnight/WhitePrincess "courtship" as they squirm on Mab's hook attempting to not-disobey-Mab (but also not have a Winter-shotgun wedding).
1a/ I
still think that Mab's primary objective (in ordering the marriage) is to throw her Starborn-Wizard-WinterKnight into the Whampire Court (where Papa Raith had Outsider-summoning rituals for his porn-starlet-sorceresses to use, his own personal Outsider-fueled antimagic wards, and where (it seems) Justine got Nemfected; and let us not forget Vitto Malvora's Outsider magic) -- the Whampires look to be absolutely
riddled with Outsider influence, and I think she expects Harry to improve that situation.
2/ Part of Harry's whole arc is a suite of power-ups to be a viable player in the BAT. The WK-mantle is a big one. I think he'll keep it 'til the end. Harry has no way to play in the BAT leagues without the WKmantle or similar.
3/ Keeping both Harry&Molly subject to their mantles keeps the Harry/Molly sexual-torment available as an element for Jim to include. No narrative tension, of course, as they
can't follow through... unless some sort of Whamp-y / etc element makes one or both lose control; the risk of that would be its own "narrative tension" (but I don't think Jim wants to play in such a rapey playground). Jim's a creative boy, though, and it's still a character-tormenting element, so I don't rule
something in this arena out of the picture.
4/ Kringle hinted to Harry (in
Cold Days) that "masks" (by which we can reasonably infer "mantles") can be put on & taken off. I think we'll see a
LOT of that in "Fight Night" which apparently has a bunch of godlings & former-gods feeding their adulation-fixation as pro wrestlers... the whole "masks" thing is HUGE in pro wrestling
5/ There are so many deep & unresolved Winter connections to explore, and the WK-mantle keeps Harry locked into them (among other things, I'm hoping/expecting Mother Winter (at some point, not in 12M) to order her Winter Knight to "Fetch me my walking-stick, boy!" (I do not believe Harry yet realizes this is the Blackstaff artifact).