AirInsight today has this piece about the possibility that Bombardier may expand the CSeries family beyond the CS100 and CS300 with CS500 and CS900 called 150- and 190-seaters. While at least the 150 seater would look like a good top end of the product line, the question is how to position it in the marketplace. If the 150 seater should have the same range as the CS100/300 (close to 3000nm), the aircraft would need a larger engine with higher thrust. Therefore Bombardier would have to raise the landing gear - the problem with that is...well, ask Boeing!
But there is another possibility: keep the MTOW at the CS300ER level - how many airlines are out there flying more than 2000nm with today's narrowbody. According to RR just about 3%.
So the CS500 might be a possibility. But I doubt there will be a 5 abreast 190 seater. This would be a too tube - just my two cents.
A driver for the 150 seater could be that Embraer thinks about a new aircraft. If they choose to place their aircraft sizewise above the CS100/300, Bombardier might be forced to react.
Interesting times ahead - Embraer should be ready to announce their plans in the next six months.
But how could Embraer pay for all this? To come up with a good CSeries competitor, they would have to be able to produce a carbon wing, for example. - Maybe they let Brasil, Argentina, Chile, South Africa and some other countries pay for it - via the KC-390 tanker development.
UPDATE: There was a suspension letter filed on October 4th, 2010 for the CS900. A 5 abreast 190-seater would have been a little bit of a too-far stretch, anyway. Or was is meant to be the name for a CRJ900 replacement? Very speculative of course...