Hello Jon,
We're not going to implement migration from gTasks anytime soon, but you may ask for such a
May be it will get many votes and we'll change our mind or there will be a volunteer who would write such an import script.
I don't think it is reasonable to rewrite Checkvist so it would keep tasks in gTasks. This could be a separate project, and we're not interested in it right now.
Kind regards,
KIR