Any aircraft design is a compromise and a choice of weighted pros and contras. You will always find a drawback. The way drawbacks are balanced against advantages may differ between different designers or pilots (and often they do....).
The NGA concept contains design challenges, such as the power shaft, the engine cooling or the fire protection, etc. NGA recognizes these important issues and will solve them thoroughly, step by step. At the end of the process, the proposed solutions will have been checked by tests.
An example of a design challenge is the transmission between the central engine and the tractor propeller using a power shaft. The shaft is designed by FEM and analyzed by software simulation. It will be checked on a test bed and a fuselage mock-up before anything else. Despite the fact that this solution may appear non-conventional, numerous other aircraft designs uses the same concept, since years, very successfullly.
In any case, the end-user will enjoy the advantages of the design and forget about the rest...