I second CoffinDodger's recommendation: there's no time like the present. You may not fully embrace GTD at work yet because of your pending transition, but why not at home and throughout the rest of your life. I would think having some of the basic habits in place around collecting, processing, organizing and reviewing when you enter this new phase of your life will only help you as a whole new set of responsibilities and projects come your way at your new job.
Also, at work, you might think about starting a "Handoff projects/open loops" project or set of projects to ensure all your current work there is properly transitioned from you to others.
However you do it, I would encourage you not to wait. DA says that the first think embraced in GTD is the Information then comes the Inspiration and onward to Installation and Integration. You've got the information and the fire of inspiration burning now. Don't lose that inspiration by waiting.