The insurance requirements alone will be enough to deter many from this market. I think that much of the target is the owner/operator replacing a cabin class twin or small turboprop (C90/cheyenne). Most of these aircraft, as mentioned have a limited payload with full fuel. The new VLJ from Piper is expected to be somewhere in the 800lb of pax and bags with full fuel. Hardly a good option for somebody that needs to get across the country with a party of five.

I doubt that these jets will clog the system any more than 172s clog the airspace we use. Like other bizjets VLJ owners will avoid the major metropolitan airports and opt for reliever airports like Peachtree, Palwaukee, etc. Also the operating altitudes will likely be in the mid 20s to low 30s, especially in the single engine models like the D-Jet and new piper model. Likely somewhere in between the turboprop and big jet guys.