There are lots of issues, but one of the major ones is that you can't get "family savings" for a suite of designs for different range/seats combinations. In the conventional layout it's quite easy to do variations (eg A318/319/320/321, or the plethora of 737 variants) optimised for different route/block patterns, but with the blended-wing concept pretty well the whole aeroplane has to be designed for a specific route and payload leading to niche aircraft with limited markets that won't service the investment requirements. This is similar to what happened to the A380, but more extreme. The concept only really seems to work with very large passenger loads, and as the A380 also showed there are only a limited number of uses for that kind of aeroplane.
Maintenance doesn't look straightforward - the engines are high-up and fully enclosed and would need fuel plumbing (presuming the fuel to be mainly in the outer wing panels) that somehow routes around the pax who are between the fuel and the engines. And I still don't see how they intend to make the pressure hull work without excessive structure weight or unacceptable stress concentrations.
And even that study report glosses over the evacuation issue by saying that they'd need to work with the FAA to produce some "new requirements". The lawyers would have a field day with that one if one ever caught fire or ditched...
PDR