What is behind the back shower wall and the right hand shower wall?

You need to post a to scale floor plan of the whole area for sure include the toilet placement since they are expensive to move . We also need to know what spaces are around the bathroom including closets in adjoing rooms. The drawing is easiest done on graph paper we need to see every window ,doorway where the doorway leads and maybe some clue as to your budget

just throwing out ideas ... a stacked washer and dryer? we have such in our master bath. I would say the master bath is not the optimal place for a washer and dryer, but I like it much better than toting laundry two floors down to the basement!

Find a stand alone cabinet/armoire piece that will fit to give the room some color/energy.

If you turn the tub area into a new large shower, consider the silhouette which may be seen through the lightly-frosted window. Is the frosting heavy enough to provide for privacy for a person standing in the shower, backlit by the bathroom lighting?

That is a really large window to go in a shower. I had a window in my shower in my last house but it was only about 18" square. You might be better off looking at the space as a whole and maybe rearranging some other elements as well. If you want to consider that, post a floor plan with measurements (ideally on graph paper). You will get plenty of suggestions. Or would you be able to change the size of the window? I don't know how easy that would be since I don't know what the exterior surface of your house is.

How about a bench? or storage to hide laundry baskets?