G7000/8000 are "delayed" - with the demonstrated efficiency of the CSeries, would there be significant sales of a BBJ-like Executive variant in their place? The airframe cost would not appear to be significant in that market.
A C-Series business jet would make sense, but not as replacement for the G7000/8000. It could be a interesting competition for Embraer Lineage 1000 and the small Airbus ACJ or Boeing BBJ. Esp. if Aux fuel tanks available. The Global 7000/8000 are ULR Jets with a range of 7.300 NM and above to compete with the latest Gulfstream Jets. And when you see the Gulfstream sales numbers the Global 7000/8000 should have been in the market since 2013.