Good question - so good it's taken me half a month to answer it.
At the moment I'm busy with quite a lot of writing projects, some Smith-related, others not. I am indeed working on a Smith 4, which will hopefully deliver the same amount of hard SF, philosophical discourse and reasoned debate (ie virtually none) as the previous volumes. I can't say for sure when it will be out but I'm hoping next year, as early as possible.
But before that happens I've got plans for the website. I'm in the last stages of putting together a Toby Frost site to run parallel with the Smith site, to contain other projects as well. That site is also going to contain a couple of chapters of the Great Fantasy Epic, which people will be welcome to read. If there's sufficient interest, I'll put up more of it.
So I hope this goes a fair way to answering your query. There's lots more I'd like to do with Smith and co, and there's also a lot of other things I'd like to write as well. I'll be putting up more details once they occur, so watch this sub-forum!