So I had an idea about how a possible update for the fade function could work:
You choose a line, and then you input the color of the text, and it goes from the first frame of the line through each frame and searches for that color. Once it finds it, the program says "this is the end of the fade-in" and sets that as the fade-in value. The same would work in reverse for fade outs: It looks for the first frame in which your given color disappears, then it says "this is the beginning of the fade-out" and counts the number of frames until the set end of the line, then sets that as the fade-out value.
If this has already been done as a plugin, I'd love to have it, it would make things incredibly easier for me. If it hasn't, then tell me what you think! Devs, would it be possible to do with Aegisub? I know that Aegisub can already do color detection to at least some extent, so it seems feasible.