I'll argue that RPT was actually a worse idea than Stone. For one thing the diversity of allowing players the choice of both mineral and vegetable PCs precludes many campaign concepts such as the ever-popular "Defend your quarry from invasion by humans filming an episode of Doctor Who".
Furthermore, being part of the larger GURPS system, players of RPT have access to rules for portraying animal PCs as well, and eventually someone is going to insist on being allowed to play a beetle in a stones campaign. While vegetable PCs cause some milieu issues, animal PCs are simply unbalanced mechanically versus mineral and vegetable PCs. The abilities of animals to move around and communicate makes them mechanically superior to their mineral and vegetable counterparts and is in no way balanced by their near-constant need for nourishment.