First objection: Try something like "Do concrete next action on Project XYZ." If you want to keep going on Project XYZ, do so. When you stop work on XYZ, determine a next action for it. A next action is like a book mark: It tells you where and how to start working on the project again.
Originally Posted by AGrzes
Second: Your hypothetical next action is then not something you are committed to doing. Your next action is then to find the real next action. Or just do whatever feels right and move on from there.
Third: I'm not sure what you mean here. GTD does not particularly embrace detailed project planning. All you need for a project is a desired outcome and at least one next action. That's it. If you need more planning, that's a next action. If you don't need more planning, don't do it.