@James, just a short idea.
If you would like to have community support not just for biomes but also for prefabs, you could ask people to design some nice things for you guys and handover to you? To make thinks easy and you visibly see what you get, maybe with screenshot of prefabs in same thread.
Even when you modify those prefabs, you could safe some time for other stuff? And if you like certain prefabs, give some topics like: trees (tropical, ancient, european) or stone formations (canyon, mountainside).. Dunno if that is handy support for you or if your designers like to workout things themselves.