"Qnatas is talking to Boeing about a big order to launch the 717-300."
"Qnatas"? I suppose even the greatest fans can make typos. Do you have a reliable source for this?
"What type of regional jet would replace the 146?"
I'm led to believe that "replacing" the 146 depends on how the relationship with National Jet pans out. Also I think they would be hoping that on a lot of routes the 146s are used that there will be sufficient growth to eventually use the 717 as a replacement. Which means there will be a big gap between the Dash 8-300 and the 717-200. Whether that is filled by a "true" regional jet such as the ERJ 170/190 will be interesting. The 135/145 is too small to "replace" the 146s.
"I told you I was ill ..." Spike Milligan