Interesting question OP.
The buy-in, for anyone who wants to play NOW at least, is still fairly high. This suggests that only fairly dedicated fans of Elite and the genre would be spending that amount - at least to me. Equally though, such fans will have been aware of Elite Dangerous for quite some time you'd imagine.
So, E3 will doubtless create some additional buzz - though I wonder if people who hide under rocks for years at a time actually attend E3

What I mean is, ED won't be news to most, I'd imagine.
I guess we might see a boost in forum numbers as more people actively follow the development, plus a fair few pre-orders might result. I'd not expect a huge jump in Premium Beta players though.
The thing is though, I can imagine ED looks AMAZING when shown being played on a big screen. There is already a fair bit of game there, but is it enough for those who really just want to play, rather than help test?
Scoob.