It's not really weird. It was actually a pretty big trend starting in the early 60s through early 80s. The fully enclosed combo kits. Easy to install. Waterproof out of the box (unless you really flubbed the install). Don't have to do a lot of work to install it and they last forever!
So here is the deal. You don't know what is above the shower. You need to open that front part of the wall up above the shower and shine a flashlight in there to scop out what is there.
Either it is full of hvac, electrical, plumbing and will require a bit of work to move that stuff around. Good new here is that the drop seems rather big so if there is stuff in this section you could surely condense it if you don't want to totally move it.
Or someone got the current kit and decided to lower the ceiling to make the kit fit perfect. If this is the case good news for you. You probably can take out that entire box and redrywall the ceiling and be done with it (might have some minor electrical going through it).
Remove some of the Sheetrock and look you probably will find an empty space there. If so have at it.
I have run into a few houses that had ductwork in those zones so there was not much I could do the boxed section had to stay.
Since we can not see the entire space the answer is possibly. Once you open the Sheetrock this should turn into oh yea or no somethings there.