It would be interesting to see NS2 provide a predefined set of "indigenous species". At the discretion of the mapper and/or server, they could be added to the map. These could be rats, mice, fish, perhaps some insects, and maybe even NS-specific species not found on earth.
These would not attack either aliens or marines, and would have a remedial AI - perhaps with a few hints from the mapper. They could move around and make noises. They could be attacked by either team, and would attempt to run away when this happens. A while after they die, they would respawn. Knowing about these species, mappers could cater to them, placing small areas (like small vents, holes, cracks, etc) where only these species could go.
What this accomplishes is provides a more dynamic and immersive playing experience, which makes it more interesting to play in the long term.
Short term, I don't expect these species to affect gameplay much. However, I can see this be extended by future releases and mods to add some of the following:
- Some species could be come pests, occasionally attacking a lone skulk or light marine
- Larger species actually show up on marine motion tracking.
- Aliens could eat the larger species to get a small amount of health.
- Species could become invasive, eventually attacking and infesting unattended structures
- Swarms of insects could make an area unapproachable by lone marines or aliens, due to risk of getting stung, etc.
- Better AI
P.S. I'm not talking about bot aliens or marines here.