According to the documentation, it does none of those things. The only thing it uses GPS positioning for is to determine your heading and speed (horizontal and vertical). Of course, Dynon could chime in to specify some capability I don't see in the documentation.
Then how does it display what is called "Synthetic Vision", or perhaps I should say, what exactly do they mean when they say "Synthetic Vision"? Is this only a horizon line with blue for sky and green/brown for ground? The image presented in the user's guide:
clearly shows terrain elevation details, and a few lakes, which certainly implies that it is positionally accurate.
That's a good question for Dynon. I'm only relating what's in the documentation, that it only uses GPS positioning for determining heading and speed. I saw nothing about terrain height, so I personally wouldn't put a lot of trust in that capability without a more specific answer from Dynon. You make a good point that the raw position data is there to potentially enable those capabilities, but the real question is whether or not they include the processing power to make that a reality. I suspect they don't, because it would seem logical they'd advertise it if they did. But there's no way to tell for sure without elaboration from them, or from someone more knowledgeable than us.
So it doesn't have a readout of lat/long, if that's what you're asking. More generally, synthetic vision IS created by using the attitude, GPS position, GPS direction, and GPS altitude, against a worldwide terrain database. So what you see in the D3s synthetic vision should be the same as you see out the window.
Since the altitude is GPS derived, it will be MSL rather than AGL. So even though you see the terrain, it won't tell you how high you are above it, which it sounded like you were hoping for. It wouldn't surprise me to see all of this someday though. They keep improving their offerings all the time. Might be a follow-on model to the D3 though. Dynon never talks about what is planned or in the works, and they do have good reason to be that way.
Does that mean that current product is not hardware-capable of being software-upgradable?
Let me rephrase. If at some point in the future, Dynon decided to add one or more features to the D3, is the current product capable of being so upgraded with only a software upgrade, or would it require hardware upgrade or purchase of a new unit?
That would depend on what feature or features they wanted to add. Technically, yes, there is at least some 'room' available for upgrades. But obviously that room isn't infinite. Whether or not there was existing existing capability to add any specific feature would require at least some development effort be expended to make that determination, so they couldn't really give a finite answer to such a hypothetical question.