I've just emailed my agent a book proposal - the first five and a half thousand words of something new, and a ten and a half thousand word outline of the remainder. It feels exciting, as new things always do.
Back now to some final tweaks on Transmission (Ragnarok 2), and then all my concentration will be on Resonance (Ragnarok 3).
So why would I interrupt the process to work intensely on proposing something new? Because my current contract is for the Ragnarok trilogy, and it's always good to know what's going to happen after that. It's a weird part of being a writer. But if I get the timing right, then by the time I'm freed up and ready to work on the new project for real, my agent will have sold the rights to a publisher, so it's a concrete project and not speculative.
I'll be keeping mum about the new thing, though. You have to keep the psychological pressure built up inside, like a pressure cooker. The only successful writer I know of who can talk a lot about a story and still manage to write it is Larry Niven - for every other writer I know of, that kind of discussion would kill the story before it's written. The reason is that discussions feel like accomplishments, whereas the story needs to be aching for completion inside your mind, pulling you along until it really is finished.
Anyone interested in psychology might care to Google "Zeigarnik Effect" at this point.