As a Roblox developer, it is currently too hard to implement text highlighting for a textbox.
Highlighting text is really useful for stuff like copying, pasting or deleting large sections of text. Right now, it takes way too long do these kind of actions. Besides the case of spending ages deleting text the Roblox chat GUI, plugins are generally a bigger case where we use text input a lot and this would make our lives much easier when using them.
tl;dr This would make I and all of the players on this platform have a better experience when using textboxes if we could highlight text along with copying and pasting the selected text.
Edit: with the upcoming(maybe) plugingui update, this would be appropriate to fit with the rest of the studio UI.
Highlighting would look like this: