With two more trilogies planned. And possibly another trilogy between those two trilogies (he has an idea but hasn’t committed. I assume he’ll do it just to get it to 16 books, which is the significant number throughout the series)
The great thing about Sanderson is that he’s a machine that just won’t stop writing. The man wrote 5 extra books in secret just because he could.
The terrible thing about Sanderson is that he’s a writing machine, and just when you think you’re caught up he drops 5 extra books on you! Still, beats waiting for G.R.R.M. to finish a book.