I only use generic characters and backgrounds (both 2D and 3D) which means I cannot benefit from Naninovel's vast collection of transition effects. However, I use shaders which support alpha and with which I can create a fade in/fade out effect using tint (#FFFFFF00 to #FFFFFFFF and vice versa) But since this fade effect happens very often, my scripts end up becoming cluttered. Currently, @animate requires that the actor be visible which means that in order to fade in, I'd have to call the actor first using @char. So the minimum amount of commands for a simple fade in effect is 2.

I'd like to propose an option similar to 'Control Opacity' found on Custom UI's that, once enabled, takes the alpha value out of the generic actor's materials added under Tint Color Changed Unity event and just like Custom UI's, fades the actor in and out depending on visibility for the duration specified under the time parameter.

I think this would be a feature that would benefit many generic users, hence I thought I'd inquire here before I start coming up with a solution of my own once my C# chops are good enough. : ]

Did you try using On Visibility Changed event of generic behavior component? You can bind your custom fade mechanics to it; other built-in implementations work in the same way.