Stephen King Opens Up the Dark Tower for Business Again

?Stephen King is writing another Dark Tower book. Specifically, about this (from his blog):

At some point, while worrying over the
copyedited manuscript of the next book (11/22/63, out November
8th), I started thinking–and dreaming–about Mid-World again. The
major story of Roland and his ka-tet was told, but I realized
there was at least one hole in the narrative progression: what
happened to Roland, Jake, Eddie, Susannah, and Oy between the
time they leave the Emerald City (the end of Wizard and Glass)
and the time we pick them up again, on the outskirts of Calla
Bryn Sturgis (the beginning of Wolves of the Calla)?

There was a storm, I decided. One of
sudden and vicious intensity. The kind to which billy-bumblers
like Oy are particularly susceptible. Little by little, a story
began to take shape. I saw a line of riders, one of them
Roland’s old mate, Jamie DeCurry, emerging from clouds of alkali
dust thrown by a high wind. I saw a severed head on a fencepost.
I saw a swamp full of dangers and terrors. I saw just enough to
want to see the rest. Long story short, I went back to visit an-tet
with my friends for awhile. The result is a novel called The
Wind Through the Keyhole. It’s finished, and I expect it will be
published next year.

It won’t tell you much that’s new about
Roland and his friends, but there’s a lot none of us knew about
Mid-World, both past and present. The novel is shorter than DT
2-7, but quite a bit longer than the first volume–call this one
DT-4.5. It’s not going to change anybody’s life, but God, I had
fun.

The Dark Tower is one of the holes in my nerd education (feel free to chastise me in the comments) but my impression has been that given the way the Dark Tower series kind of fizzled out, another book would be more aggravating than anticipated — especially a book that takes place in-between the other books. Am I wrong?