I don't know if they will, but if they do, I don't think it will be considerably different than the version published in 2007.
I was one of the peer reviewers on the original edition (with a different name), published in 2005. The next edition after 2005 was published in 2007; my best guess is that the new version of Open Mouse might get published in fall 2009.
I have looked at the 2007 version and other than a few updates, it's not really much different than the 2005 version. I would just get the 2007 version rather than wait for a new one that might not come out until after you are back from your trip.