Something that I’d like to see is the ability to reflect images along either its X or Y axis easily. I understand that this can problem is some-what already solved; changing the ImageRectOffset and/or ImageRectSize values takes care of the situation. However my thought of flipping the images would be checking a box that would do the said action, or bringing a drop-down list that a player can choose which axis to reflect the image off of. It makes it easier for the developer and even easier for new creators who want to experiment with UI design and such.
Here’s a list of image-based objects that can really benefit from this property:
ImageLabel
ImageButton
Texture
Decal
Etc.
These may also greatly benefit from this property:
ParticleEmitter
Beam
Trail
[EDIT: Moved to Client Features]