This is an idea for another related mod, for which this mod provides lots of the ingredients (and more explicit details I what I think Reiver is also talking about).
Mod would be an atmospheric version of autorove, called say autofloat, with use cases long airplane trips, lighter-than-air airships (using negative weight airship parts someone will need to make), and most exciting for me: Eve floating cloud cities!
Requirements for the mod:
allow activation for vessels that are in atmosphere, not moving vertically more than say 2m/s, and not accelerating vertically much either, i.e, stable altitude
modify KSP behaviour to allow swapping focus away from this vessel, and when it does so, prevent the vessel from being unloaded (ie destroyed) -- there are mods that eg extend physics range, so I guess looking at how they catch the atmosphere unload step would help. This is probably the biggest new work compared to autorove
on swapping focus, take a snapshot of the horizontal velocity of the vessel compared to surface -- that's the speed of the craft. Assume altitude remains constant
move the craft at that speed towards target, and also have an option to not require a target, in which case just continue to move the craft on current velocity around and around the planet (useful for airships, cloud cities)
when user swaps back to craft or physics range of craft, restore as autorove currently does (though obviously in atmosphere, not on surface)
So main change compared to autorove is to catch and change KSP behaviour when trying to swap focus away from atmospheric vessels.
Shortcomings: this obviously doesn't take fuel into account, or aerodynamic ability to change direction and hover/circle at destination. One option (for version 2) would be to check flow rate for fuel, and only allow activation if it's zero (ie require electric propulsion or lighter than air parts), or even reduce it over time that the craft if moving.
So yeah, hopefully Wotano or someone has time to do this! Unfortunately I don't have time or skills right now