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.
I am in the market for a new digital Camera. I will be oversees for a year and hope to get some great pictures. I have also recently begun using editing software to make short films, and it is something I look to continue doing.
With that in mind I am looking for a camera that has high quality HD video but can also take great pictures.
The problem is that I am by no means a seasoned photographer. I have little experience, and am anxious to learn. I was looking into entry level DSLRs such as the Canon rebel T3i or 60D. It would allow me to take great pics and vid fairly easily if I desired, and also would let me learn how to use the advance settings over time.
But there were also cameras in the category of prosumer compact, or interchangeable lens compact, that might suite me better. However it seems that many of these cameras are in the same price range as entry level DSLRs and I don't see any reason to buy them if I could get a DSLR that would allow me to grow with the camera.