Discussions on the CS by CityJet were only to get a better deal from SSJ.
Sure... try go get a discount from a vendor by threatening to buy a competitor's product
twice the cost... that's sounds like a winning negotiation strategy.
If anything, they were bringing E2 and SSJ into the equation to try to extract lower price from Bombardier -- the most expensive vendor at the table -- not the other way around.
My own belief -- CityJet tried to make the CS100 work -- configured for ~110 passengers -- but the economics just weren't there. For new longer routes it would make sense to fly a larger aircraft, at least a CS300. For shorter routes CityJet currently serves, the CS100 is twice the cost but offer marginal operational improvements vs the E2 or the SSJ, especially with low oil prices.
So the CS100 was not competitive and lost out. CityJet might take a second look at the CS300 when it becomes available. They'd sacrifice commonality but the bottom dollar line is what counts for the bean counters.