Yes, I would love to see procedural terrain in orbiter. I think, the possibility to implement procedural or rules based friction coefficients for the surface terrain will also improve the realism by a great amount, for example, runways and taxiways will have a relatively smooth surface to allow proper taxiing. But the rest of the surface should be much more rough to simulate crashing when the craft goes off the runway at high speeds. I remember I used to run the DG at 300m/s over the surface of the Earth in 2010?
Also scripted bases, like face's ascension ultra project, but maybe implemented through Lua instead of a hard coded dll. It will make the orbiter universe come alive and make it hugely interactive. In that way it can persist across scenarios, and not be a vessel to be loaded in the scenario.
Regarding scenarios and surface bases, I know there is already a provision of time periods, where the bases will have a different configuration based on the date in the sim. This can simulate historical events more accurately, and to improve the immersion and realism, the terrain and textures can be also made to change with the date
The stock base building elements provided by orbiter can be expanded and made more useful and detailed and interactive as well, which ties into the concept of scripted bases
Also, improving the collision and damage failure simulation is a high priority.
Eventually we may have "surface bases" in orbit, which is to say, fancy space stations which persist across scenarios
For the rest of orbiter, I will say that orbiter already does a great job of simulating celestial mechanics very accurately, but still there will always be room for improvement. Maybe relativistic effects can be added later.
D3D9 will become the primary graphics engine, unshackled by the limitations of dx7. The current d3d9 client is mostly a wrapper for dx7 calls, with added goodies. A graphics engine built from the ground up for d3d9 will be great! It could be improved later with built-from-scratch vulkan client as well, with volumetric clouds in multiple layers and fog, maybe finally helping orbiter go multi threaded and 64 bit and platform agnostic