Mostly I just think it'd be nice to plant the seeds on top of things like Farmer's Delight rich soil or tilled dirt variants from other mods that use their own dirt types without expressly needing to 'import' some vanilla dirt to set up a farm in areas that might otherwise lack it.

That said, I would say it would probably be wise to somehow manually add a means for unique crops to "ignore" any effects of predefined soils that provide extra growth ticks to things planted on top of them since that would probably cause balance issues.