If Harry gets out of the Winter Knight's gig I can see him becoming the Blackstaff, something that would go against his grain even more than being Winter Knight ... 
I expect the WK-Mantle and the Blackstaff to play together in all sorts of "
interesting" new ways for poor Mr. Dresden.
I expect Jim to dig that knife in and  
t-w-i-s-t  it.
I expect Eb to fall in battle (probably against Outsiders), at/near the end of one of the novels, and Harry to pick up the Blackstaff right there, out of necessity, to wield it and end the battle.  But hey -- maybe that microfiction-tease'd fight with the Cornerhound is where Eb falls?  (Eb is a heavier hitter than Harry is; MUCH heavier.  I can't see Harry handling something that overpowers Ebenezer... except Outsiders.)
 ... However I don't see him getting out of it, I think it is too important in the fight ahead ... 
Agreed.  I'm not clear if Mab's strategic goals for Harry involve 
her wielding a Starborn Wizard Knight against the Outsiders... or if she is finding a way to 
give the Winter Knight's mantle to a Starborn Wizard, for him to wield (more or less independent of her orders) against the Outsiders.
Possibly she sees both outcomes as acceptable.
What I think we will see is Harry will learn how to "take off" the Mantle at will; it's still 
there, still 
his; but he won't be the Mantle's, and he will have other things too.  Vadderung, after all, isn't ALWAYS Kringle (and very well may have another Mantle -- or several -- he sometimes wears, as well).
From a Doylist POV, for Jim's writing, I think we're seeing a bunch of anti-Outsider stuff getting added, bit by bit, into Harry's repertoire.  Soulfire is a bit of that origin-of-the-universe Creation energy; what better tool against anti-Creation Outsiders?  Winter powers... and 
Winter is the primary anti-Outsider combat force.  Warden of Demonreach.  Willpower (over and over again, Harry's willpower keeps getting more and more severely tested... and strengthened), which seems to be a key element in breaking Outsider's "psychic whammy."
Come the BAT, I expect all those tools will be available to Harry.  (I do include, BTW, 
Hellfire!  Harry doesn't much care for it, or use it; but I think he still has 
access to it, and 
WILL use it in the BAT).