I think these technologies are developing exponentially, and in many cases, are far more mature than you'd think.
Tail - sitters seem to be the way to go, and the fcs issues appear to have been cracked.
If a few blokes in a workshop can do this;
https://www.suasnews.com/2017/04/heu...ch-tailsitter/
..then I'm not willing to bet against NG doing likewise, albeit on a much bigger scale. The rest appears merely (!) to be the integration of already extant technologies.