I don't think you will "need" to upgrade. I would thing the 6xx series will be good for quite a while, at least just to receive TV. I think that the 6xx can do whole home, plus eSATA DVR expander, ad maybe Shaw VOD.
Whishful thinking, is that they would totally make Shaw Direct compatible versions of the DirecTV HR22 platform, which uses at least both SWiM (Single Wire Multiswitch), and coaxial networking which they call DECA. Or at least their versions of the same thing.
The other way would be to have a four tuner DVR gateway box, and the same client boxes the Shaw Cable gateway uses.