We can expect the Fomor to return.
Also, though it is gone, my road map does point to the Raiths and Mavra being involved in the plot.*
Gotta figure the emphasis on Thomas and family will finally bring a big scene between the two brothers and their grandfather.
And given that, Harry and Molly's relationship with the White Council and Winter Court will likely come up.
* Not going to put the whole thing out there, but the gist was that the first ten books laid the outline for the next ten. In books 1 and 11, Harry fought an evil wizard breaking one of the laws. In books 2 and 12, Harry took on dark power to face a bigger threat. In books 3 and 13, Harry fought super ghosts. In books 4 and 14, Harry fought crazy fairy princesses. And in Books 5 and 15, Nicodemus was after a Catholic relic and Harry teamed up with paladins to stop him.