Yet another example of You Never Know Where Ideas For A Piece Will Come From.
While at Toys 'R Us with grandson Will and his little sister Katie I came acrossed this.
619 parts, including an Eyes Light Up and Roars part, a Battery Pack With Switch, A Motor Module and a Gear Box Module - and - a bunch of THESE
which let you do stuff like this
which, in turn lead to this initial idea.