"Which way is down?" - UI and UX polish needed

With the many recent pushes for fleshing out planets, I feel that one important sense is neglected, or rather covering the absence of that sense due to this being a computer game, not real life, is neglected:

The sense of DOWN.

The movement-sensing organs in our ears and the general feeling of weight in our bodies is completely disabled when looking at the computer screen and controlling avatar or ship and seeing nothing but textured polygons. Worst offender: Mining, planetary in particular.

Problems:

Translation aside, control inputs are left-right and up-down, which is fed back to the player in the form of optical flow, and optical flow alone. As the display screen is typically flat and occupies only a marginal fraction of typical human vision's FOV, the display alone is not suitable to easily convey a measure of rotation, either. It is therefore reasonable to assume that, for the player, it is practically impossible to keep the ever-compounding various Eulerian rotations during gameplay in mind to always compensate for the resulting tilt in the craft's or avatar's left-right rotational axis against the gravity vector, g⃗: For example, when swiveling drills through an ore vein, "rotate up, rotate left, rotate down, rotate right" does not return to the original orientation! A mining craft may begin to lean until it exceeds the capacity of its side thrusters and crashes. And while this can be compensated in-game by adding stronger side thrusters, such measure is more compensating for a shortcoming in usability than a real measure that would be natural in-universe.

This is compounded by the lack of GUI contrast: The artificial horizon is an extremely weak, low-contrast white-blueish line in the middle of the screen that easily drowns in bright, busy scenes such as an ore vein illuminated by the mining craft's spotlights, a feature commonly added to player craft. There is also a smaller artificial horizon in the toolbar near the bottom of the screen; however, this one is extremely small and far away from other visual cues (or lack thereof) in the centre of the screen, thereby rarely visited by the player's vision, which greatly diminishes its effectiveness.

More screenshots to illustrate the issue: https://imgur.com/a/gmEIUMK

To correct for the tilt, gyroscopes are an obvious and readily available measure. However, while gyroscopes are easily capable of producing high rotation rates about pitch and yaw axis, often close to how fast the mouse is moved, the rotation about the bank axis is pretty much fixed, or capped, and bound to keys Q and E. It is this detachment that makes correction for tilt very tedious, if not impossible in extreme situations.

Challenge:

SE UI and UX should receive a significant polish to compensate for the disparity between player-sensed gravity and in-game gravity and the lack of accountable cues for it.

Proposals:

• Must have: When rotating an avatar or a ship within a gravity field, the left-right mouse input should translate to a rotation around the parallel to the gravity vector g⃗. This also benefits from FPS and 3PS experience the player may not unlikely have gathered in other games, preventing or diminishing a retraining effect which in turn makes the game more accessible.
  
  (Visualisation of free and constrained rotation. The green arrow shall represent local g⃗ within the gameworld, the tilt against the view shall represent the player's current view angle against the gameworld. Left: Player avatar rotates about its local "up" which may easily be aparallel to local g⃗. Right: Even though the view is tilted, the player avatar rotates about an axis that is parallel to g⃗. (Image source))
• Must have: This constraint should be freely togglable.
• Nice to have: Toggling the constraint should observe the avatar's or craft's current axial tilt against g⃗ whenever it is toggled. No auto-reorientation should occur to prevent collision with environment.
• The artificial horizon should be made more prominent. Make it larger, more centered, and more robust against drowning against the in-world scene.