Surely to goodness nobody would ever think of dreaming of doing that?
This philosophical debate pops up every so often
"Officially", if you are not VMC then you are IFR.
And if you are IFR then you are "officially" supposed to fly
IFR procedures ONLY.
Which, in turn, makes all this new fangled stuff "officially completely useless".
QED.
So......... what shall we do about the hundreds of "professional" pilots, flying 2-crew airliners, with fantastic currency, supposedly fantastic official training, gold plated ATPLs, who sure enough knew about approach plates, missed approaches, and all the decades-old IFR paraphenalia, and who still somehow managed to fcuk up big time and splattered their jets and the contents of xxx passengers into some mountainside?
That is why GPWS has been mandatory for many years, but it did not really work until a GPS-assisted EGPWS version (with a terrain database) came along because terrain clearance in the old GPWS was really just based on a radar altimeter, which is not much good if you are flying towards a mountain. Read that famous Mr Erebus one, 1980s sometime, for one of many examples.
So, terrain awareness based on a terrain database and an electronically derived position+altitude, is absolutely not just recognised but is mandatory in big PT stuff - but only as a last resort. To use it to fly what will - in most airspaces - be illegal IFR (VFR in IMC) is not legal and never will be. Let's face it, most places do not even support or allow IFR OCAS, etc.
I suppose one could use it legally for night VFR in mountains, because a pitch black night is not "legally IMC" - believe it or not
Scud running is perfectly safe until the pilot enters IMC and either loses control or does a CFIT, or ends up boxed in by terrain and hits something when trying to turn around. (A bit like flying is 100% safe; it's only a crash that is a problem). I don't see how SV would help there, other than facilitating illegal VFR in IMC.
Now, VFR flight in IMC is common all around the world, because most pilots (even in the USA) have only got a bare PPL. I suppose that, in years to come, SV will make this an accepted way to fly around, enabling the pilot to ignore the concept of MSA to the same extent that real-VFR pilots routinely ignore it right now.
This might not be unsafe if one is doing it in one's regular neck of the woods, where the terrain database has been tested in VMC on previous flights.
Technically, IF the terrain database has been verified, such VFR-in-IMC flight won't be any less safe than flying any instrument approach (all the way to the DH/MDH i.e. below MSA) in IMC, be it based on navaids or GPS/WAAS/EGNOS.
As regards a failure of a big LCD panel, yes this is probably much more likely than losing half a dozen individual instruments (be they steam gauges, or electronic "EFIS" versions) but what would concern me more is the difficulty of getting this stuff sorted by your friendly little local avionics man, or even by yourself (and signed off by somebody). I have a huge collection of avionics installation manuals but have never even seen anything on the Garmin glass stuff which is obviously tightly held and only made available to Garmin dealers who are authorised to work on the specified products. Aircraft ownership is peppered with barrels (for you to bend over) and a glass cockpit in the biggest barrel of them all. It's OK if you are based at Bournemouth/Cranfield/Cambridge/Southend/Biggin/Booker where the dealers are...