It depends if it goes through an upgrader in Canada first. The production that is shipping Bitumen is diluting it with Naphtha or the like first, referred to as Dilbit.
There have been several bitumen upgraders built in Canada and more planned. With this process a rather high grade of light Syncrude is produced.
Essentially the problems you discuss with heavies are a problem for the pipelines as well. Meaning that the heavy gravity issues are already resolved.
The volume issue still exists. This would have to be broken up to many different refineries every day to be handled. But the pipeline would do the same so also no real change.
Cheers