There were talks about tail sitters multiple times, and I can't remember anybody objecting them, so I guess it's a nice little feature to work on.
And as a bonus, I tend to make ships with this at least in the back of my head, so most of the ships won't really suffer much, if they are made able to support this feature. (A few months ago for some reason I doodled almost all ships in this way, for my curiosity, while I was sitting on the subway.). And there could be ships that won't be tailsitters ever, and vice-versa.
This mod has a Mola that has both belly and tail sitter configuration, and rudimentary animation/mesh for it.
Admittedly it's not pretty, far from it, but from my side it should have everything needed for it asset-wise.
- I got an error message that two animations are trying to control the same object, so for now the fins around the engines won't be rotating away when the tail gear lowers, and they will stick into the ground. Which is a problem, since there are quite a few ships that have those fins, and they are a feature I really like in them, so I'd rather don't ditch them if it's possible. So I guess that needs to be addressed for this to work nicely.
- The animation for lowering the tail gear is called "tail_sitter" and it's from #101 to #200. It can be checked already in the model viewer, if you select the animation for it from the drop-down menu.
- The tag for it in the model is called "tag_tailsitter, and it's oriented similarly to tag_landing, but rotated 90 degrees on X: Y is up (nose), Z is top, X is right. So -Y points towards the landing pad.
- You need to delete the sgm file of the Mola Mola for the mod to work. (I have to look up the command and start including sgm-s with my preview mods I guess.)
My reasoning is that in most cases it's easier and more convenient to load/unload a cargo hold in a belly sitting configuration, and the engine technology is clearly available to support it.
And on low-G worlds, it doesn't even matter that much anyway.
Also this configuration is more familiar to most people since it's the default for almost all movies and games these days. Not to mention real aircraft. (this alone won't be a good reasoning to me, since these are just conventions, even trope, but good to mention it anyway. And the presence of tail-sitters along belly sitters would also provide a nice contrast and a way to hammer the tail sitter back into the general consciousness.)
Also it's not unheard of even here on earth to have a deck that works in both conditions (can't recall the name of the ship that can flip itself, it's some kind of research vessel, it should be somewhere in the Inspiration or sketch thread). It might be balanced with giving much worse exhaust velocity to the belly engines, in exchange for the increased thrust, which would also facilitate decision making for the player, if it's clearly communicated.
And form another pov: I found that it adds a nice bit to the maneuvering for the ships: Having strong belly thrusters makes the ships more maneuverable pitching up (in regards to moving the prograde vector) which actually provides a more organic incentive for rolling during combat then nerfing the yaw as in Elite Dangerous.
EDIT: Another good point for tail sitters: Set Speed mode already can be used to hover down backwards slowly, which makes landing quite easier. (But on the other hand, some kind of similar hover autopilot mode for level flight would be a nice touch.)
Other stuff to note: As far as I know there's nobody around here these days who really knows the autopilot code, so this whole thing might be quite a bitch to figure out, but let's hope it's not.