While this is certainly a feature that would benefit the engine by bringing it up to industry standard, it would be more of a quality-of-life improvement for the developers than anything else. Currently, it is not at all all hard to change a Color and Transparency property at the same time. I would even describe it as simple and easy. This is evidenced by your example:
You mention that it requires “a lot of extra work” in order to accomplish this when it only takes a single extra line compared to your proposed solution. Additionally, the extra line isn’t even complicated in the slightest, merely being a simple property assignment. Therefore, although I do support this as a quality-of-life improvement, I don’t believe it’d be significant enough of a change to warrant the developer team to implement anytime soon.
I do admit that this would make utilizing EditableImage’s easier, but, as I stated above, not significant enough to implement anytime soon, even though I’d support it. Especially when, at the time of this posting, Color3 values still don’t support basic math operations.