Alright, I have an idea to convert the symbiotes and parasites from Rifts: Atlantis and Rifts: Splynn Dimensional Market to Starfinder. Although, sadly, my books are in storage and I can't attempt it.
If I remember correctly, Palladium doesn't allow conversions to be published either, but he (KS) has no bite anymore. Maybe I should wait, but it would be cool to have a living heart.
Whenever I get a Starfinder Campaign off the ground I will definitely be pulling stuff from my Rifts books for my games.