I don't think you should hold to a promise like that! Even if you had wondrous plans for this series, the content you've made already is substantial enough to stand on it's own, in my opinion.
If you're really hellbent on sharing more of this universe, why not try another medium, even if it was just in actual text only fable form? It would also be very suited for a Choose-Your-Own-Adventure format text game.
Like I said though, what you've done already is more than enough. There's no point in burdening yourself with any promises that aren't doing you any good, you owe nothing to anyone!