Hi guys! I'm the project lead for Heaven Variant, but I also peruse the HLP forums (I was apart of a few of the voice over FS2 projects back in the day (Shadows of Lylat and beyond the red line). Thanks for the link post!
The visibility of stuff is something I'm watching closely. In- game though when we've been testing it, visibility hasn't really been an issue, but again, we're watching it closely. For instance, whenever something interesting or distracting is passing by, we're making sure not to have a lot going on, especially bullets, which largely occur only when lulls in the background are passing by, so in a way we're working on getting the backgrounds and bullets all synced together. Bullets have a lot of enhancements on them so that they're both lit and project shadows around the bullets so you can see them whether they're in very dark environments or super bright ones, and they'll always project on top of everything else, even if a ship moves in front of it, so you'll always see everything. And once you're in game, and you're in control of where your ship is going and you have a full resolution (Without the awful video compression on our youtube vid) everything is pretty easy to see. With all of that said, so far our testing hasn't shown any real issues with visibility, however i'm watching how things develop and I'll be keeping my eye on it very closely.