Right now, leaf piles only spawn below vanilla trees which can leave modded biomes feeling empty. I dont know how difficult it would be to check what mods have leaf blocks and work back from there (potentially automatically?) but there are several commonly used mods that add leaves such as biomes o plenty, biomes you'll go, quark, premium wood, etc.
It would be nice if there were leaf piles for these mods

It's planned. Will support all leaves

Added on forge

not possible for fabric