Aside from the fact that it would be complicated and questionably practical to make in a game jam context, I wonder if some kind of trajectory predictor would work for displaying progress. A little globe or something with a curve showing where you would go if you just turned off your rocket and coasted. You could watch it climb higher as you accelerated upwards, and then widen as you accelerated horizontally.
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Cool idea! I was planning to implement something similar that just renders a partial ellipse as an orbital trajectory once the altitude was sufficiently high, but I didn't have enough time. It would be cool if such an indicator could also take air resistance into account such that the trajectory starts going down towards the earth if it gets into the atmosphere. I don't know if I have the physics expertise to do such a thing, but I might try later!
Air resistance would be tricky to model, but there's probably a simple calculation that would let you show a rough trajectory based on your current velocity. I'm not sure if I know what to Google, but the formulas for projectile motion and/or Kepler's laws of planetary motion might be a place to start?