Better GUI interface please!

It would be awesome to make certain images act like other things, such as item slots or buttons, without having to stick to the original format. I know item slots already can be colored, but it would be awesome to have custom images within the item slot like the dye or banner slots on a loom, or to just be able to have better or more custom looking buttons than the text format one provided (For instance be able to make arrow buttons for switching GUI pages instead of having to type a ">" and live with that being your arrow button. It would also be nice to be able to animate some things better, for instance making "gliding" mechanics instead of having to make eleventeen thousand different images and putting them all in the path of its glide and making a bunch more procedures with certain conditions just to get one gliding affect. It would be so much better if you could say something like: If procedure=true, glide to X:___, Y:____. It would also be nice to make some animated textures only animated on certain conditions, kind of like "costumes" in programming, to where its still the same image, but they don't only display on certain conditions. (like the flames of a furnace fire, or even outside of GUIs, the loading of a crossbow, ETC)