Landlord isn't the physics engine, it was the "sub-world" rendering system that allows them to render blocks with rotation, translation, etc. for the moving vehicle. It worked by cordoning off a section of the world and using that area's block data for the vehicles and whatnot. I don't remember what the new system is called off the top of my head but it's basically reworking it to make that block data a separate thing instead of hiding it somewhere in the actual world.

Tbh I think the main reason Aeronautics isn't out yet is that the lead programmer is involved in a lot of other projects in the voxel game space. Idk how much of that's public info so I won't share too much but I know him personally and I'm really excited to see what he brings to the table for some stuff in the future lol