Disclaimer: I'm an aerospace engineer but I don't work for Dynon (or anyone else in the homebuilt industry)
I think people are asking for two different things.
One is for the vertical component of an approach (glideslope) to be incorporated in the HITS boxes, like the current "to the runway" feature except using the vertical profile from a certified nav source.
The other is looking to be able to put in a flight plan in Skyview with altitudes, and then have Skyview "ramp" the HITS boxes up and down to the programmed altitudes.
These are different because of the way the vertical guidance portion is defined. For approach/glideslope, that's basically a fixed angle from a fixed point, so it's always going to be the same path in space no matter how fast you fly, how much power you have, or how maneuverable you are. It looks like this one is on Dynon's list for the future.
The second seems to be looking for full VNAV capability, and that's a lot harder to do. Are your climbs and descents defined by flight path angle, vertical speed, or holding an indicated speed? What power setting? How do you program this so the same feature in the same software works on a laden VW-powered Sonex and a lightly-loaded Rocket--and then works in those same airplanes when the former is light and the latter is heavy? Then, do you move the boxes along if I'm having trouble making the original climb/descent, or do you leave them in the original place and I'm always "behind the curve"? What if you base it on vertical speed, but then your airspeed changes? Redraw the boxes?
Large aircraft have these VNAV features in the FMS, but those features are built upon having a good known performance model for that specific aircraft type (which should be consistent across all such aircraft). They also typically have an autothrottle, or at least a means to display a requested power setting (sort of a flight director for the throttle). Our homebuilts may not even be consistent between two of the same model of aircraft, and I don't know of any homebuilts with autothrottle (and until we either get single-lever engine controls, or at minimum automatic mixture control, you probably won't see any).
That's why the boxes only display at the selected altitude in "normal" flight (and IIRC that's how they do it on G3X and AFS too, at least)--there are so many variables that can affect the way the boxes would be drawn that you can't feasibly do it on a "universal" avionics install. At least doing this gives you a "here's where I should be next" target that you can fly to as best as your aircraft allows.
From an engineering standpoint, yeah, a full VNAV capability could be added. It would cost Dynon a whole bunch of money to implement and test, and then to actually be able to use it right you'd have to do a comprehensive, detailed flight test program to get lift, drag, and power numbers specific to your aircraft. Most people wouldn't do that, and then Dynon would be getting a never-ending stream of phone calls and emails about how the HITS boxes aren't working right and their airplane can't make the climb that it's calling for.
