Nokia has been open about their position on this issue in the past. The next update will be released as soon as it's ready; that is, as soon as they are confident about the quality and testing issues have been resolved. They won't give a solid date because they will hold it back if there are any issues, or release it if there aren't; they can't know when that will be very accurately ahead of time. If they did announce an estimated release date, that would certainly be misinterpreted as some sort of promise or guarantee.

Edit: I realize this is not normal policy for a commercial product, but it is much more in the style of an open-source product, which to a large extent, Maemo is.