Introduce new tool, called "ceiling". The principle very similar to Curtain Wall. Interaction with lights and another MEP elements.
Introduce new global levels - FCL (finished ceiling level). Elements can be linked to FCL (light, grilles, duct systems etc.)
Have a Gravity option to snap to the underside instead of the top?
And add the option to Gravity to Curtain Walls?
In that way you can have as many different ceiling levels as you want or even slopes and not have an issue.
Gravity to curtain wall? I'm not getting it, to be honest.
I imagine floor finished level as global level, that can be accessible via new ceiling tool (and linked to it, the same way how now you can link wall to the floor level, or it's top to floor above). Then you can link your lamps to ceiling level (instead of floor level how it happens now). As well ventilation grills and smoke detectors. Top of partition walls in some cases can be linked to ceiling level. If you are changing ceiling level (that happens actually sometimes in the projects on the late stages - when something does not fit and it's necessary to drop the ceiling) - all elements associated to it changing their level too.
Because new ceiling tool based on the same technology, as stair or curtain wall, it has all members as separate GDL objects and everything can be schedules - frames, panels, hangers.