The new alpha channel export and direct alpha channel PNG support are fantastic…
One observation… many years ago I used to use Art-Lantis, it had an alpha channel export which I believe was more sophisticated… instead of rendering as black/white it also rendered shades of grey depending on how many layers of “transparent” object were in front of the background.
So, for example, if you were rendering a view looking out of a building the walls would be white (solid opaque), window glass would appear say 50% grey (partially transparent), and an open window would be black (fully transparent to the background). Likewise a view of a building from outside might have shades of grey where the background is visible through two or more panes of glass…
The advantage, in a programme like photoshop, is the alpha channel can be used to select with levels of transparency, hence a background can be inserted in a way that retains some appearance of reflections etc… on transparent and glass surfaces.
Something similar could probably be achieved combining the current alpha channel and materials export. For it to work perfectly the alpha channel would need to be calculating transparency levels for materials in front of the background - maybe more processing?
Is this something which could easily be incorporated?