----Doubts----
I don't think the full fledged biter-players vs colonist-players scenario would fit here.
Actually, I don't think pvp in general is the thing for factorio.
You see, to me it's a game about the player, complicated systems and various interactions between them. And players trading all the manners of sucker punches o get onto each other hardly harmonize with thoughtful creation of anything. Also, given that average interesting factory takes at least 6 hours to build, I doubt that players would be in for the risk of losing all that progress.
---Ramblings---
Though speaking about interactions between systems, I could see this improving currently poor environment ability to push back on the player.
There is a game called zandronum, basically it's engine for various doom2-like games with various gameplay regimes, among those there is the multiplayer regime, where a few players play for demons side, but they do not just be demons, they are puppeteers. They fly around in spectator mode and interact with the game by spawning monsters and power-ups instead of directly opposing marine-players.
And then there's that new trend in games about invasions.
---Raw stream of thoughts---
Something along these lines could look interesting addition: you log onto server, probably a while later than human players, get a nil-character and then one of following may occur.
- 1.Maybe you become an combat-adviser and tweak their attack routes so they don't just run past bazillion of turrets and then log off.
2.Maybe you can get to be a chief-spawner at some base and order nearby units around trying to drive players away from you.
3.Maybe you get elected as a president of Biterland for a limited term and get to give orders all around map, but the seriousness with which biters take your orders depends on how much pollution is there.
To give you something else to do you can smuggle the pollution to the distant bases to convince them join your fight. For example you send squad of biters with sacks to a polluted area, they collect air samples, and if they manage to get from there to unpolluted village, that village will lend units based on both the amount of samples and severity of pollution in the samples.
I'm not sure why players would want to participate in that for any significant amount of time though, unless Albert writes more motivational posts for people to join biter protection association.
Also, this all still won't make much sense while player can just waltz through a dozen bases with a shotgun, the combat would need to be shifted from the "player fights biters" to "factory fights biters".
---Final remark---
Wow, got a little carried away in the previous section, depending on how things balance out I myself may be not up for the third and even second variant suggested there.
Finally this seems to be feasible with cripts, albeit people say unit orders are unwieldy now. And probably not by me. Not in the next few months at least.