Link/Group Elements Together
One thing I was thinking that might be useful would be to link elements of a score together, so that a change in one element effects the other. This would be analogous to something like Microsoft Publisher, where you can group multiple independent objects, text boxes, etc. together so that they become one group, so resizing effects the larger group instead of individual objects. Further than this though, I also think applying this to the "inspector" window for certain things -- especially text -- could be really helpful, such as if a score requires special measure number formatting which is consistent in relative position to measures, that one could at the start of the score, move all measure number positions, lock them to their relative positions to the measures, and then when the measure changes shape, the measure numbers automatically move to be in the same relative position to the measure.
Hopefully this all makes sense; I don't imagine this would be an incredibly high-priority thing to implement, but I think it would be a nice quality-of-life feature.