Any interchangeable lens system will allow you to grow; only a very small number of people actually need or will use the massive number of lenses and other accessories that Canon or Nikon offer.

While video quality is high with DSLR's, autofocus continues to lag behind. If you will be taking a lot of video, but not using follow focus, you're probably better off with a compact system camera, or Sony's SLT cameras, which video autofocus far better than DSLR's.