Two ships flying in what looks like a realistic dimension fight. Why is this relevant? Because they didn't jitter about therefore indicating there was no lack of precision which means that they have implemented the code from the off to be 64 bit to allow the precision needed to model a galaxy.
There are many different techniques to modelling a large seamless galaxy (besides which most games only work at 1 solar system at a time level and elite dangerous probably won't be any different there). You don't need 64bit precision (within one data type) to do it without jitter.
Does that mean Braben can't pull it off. Of course not but let's be realistic here this is a task that has not been done before, is absolutely immense and has some major major technical challenges to actually even get some of the stuff promised working and working well eg seamless space to planet transition.
That is why am I am sceptical because I fully appreciate the complexity of what he is proposing and because after this time he seems to have less to show for it than other people following down the same path.
Then why not show it? That Josh Parnell bloke doing that Limit Theory has got more to show for just 3 months work (although he appears not to use realistic distances from his video).
Showing off under-lying mechanics with placeholder assets doesn't really show off to the general public very well.
David hasn't made a habit of making promises he has no intention of keeping so I believe hes confident he can pull it off - whether he can or not is another matter but I'm playing wait and see for the interim.