It means that you're going to lose what little you have left much sooner than originally planned as the move away from Anik F2 (that you can receive) to Anik G1 (that you cannot receive) will be moved up from 2025 to ASAP.
HEVC is the next generation compression standard that offers a number of enhancements over AVC. HEVC compression is 50% more efficient than AVC, which translates into maintaining the same video quality at half the bitrate or double the video quality at the same bitrate. The only way Shaw Direct (SD) can be successful in migrating all of their HD programing onto a single bird (G1), is to go to HEVC.
There is no question that HEVC has benefits (although claims of relative efficiency in a "live TV" reality are always suspect). HEVC isn't the only way but it is the probably the most desirable way given what Shaw currently has at its disposal.
Unfortunately, the timetable has been very tightly squeezed and what Shaw thought they had three years to accomplish has now been whittled down to a few months. If they can't see their way clear to execute in a wholesale upgrade of all of the older receivers in the wild, they'll have to make other compromises that will allow them to use older equipment without Anik F2. This could come in the form of lowering the bitrate (enabling them to fit more channels in the same space) or temporarily making some channels unavailable to those TVs not outfitted with an 800 series receiver.
I would recommend against using the term "SD" in reference to anything other than "Standard Definition". SD and HD are just too deeply embedded in the vernacular to be re-associated (even temporarily) with Shaw Direct and Harley-Davidson.