It would be nice to have the option to add custom plants and bases for ones that aren't automatically supported. Taking Farmer's Delight for example: it would be great to have rice work in the jar (but only if you put in a bucket of water) or for the mushroom colonies to output more mushrooms than a regular mushroom would. And if the rich soil was used instead of the regular dirt, the output would be faster than normal.

I know you could build in support for different mods but allowing modpack makers to specify stuff would allow for more flexibility. Like we could set it up so that if a sapling and a magma block were placed in the jar, charcoal would be the only output.