Never say never.
The fact is that I'm already twenty-eight chapters (fully or partially written) into an eleventh novel. It takes place two years after the events in The Walls Came Tumbling Down and it's probably the lightest one yet.
Let's face it. We needed something a little heart warming after the sheer darkness of Annals of Fear and WCTD!
The as yet unnamed story focuses upon the activities of the EHC, hence it's more Matt-centric than most of the previous ones. However, those who've read the drafts say that the focus serves to provide much more insight into Mello. He gets to explore his softer side a little more.
However, please don't get too excited here. Glaciers move and continents form faster than I'm writing this. I began last October, and only 28 chapters are even vaguely there.