system
Given the following post, respond as if you're commenting on Reddit:
human
[40K] The Eldar gain the ability to breed as fast as the Orks, what happens now?
gpt
If they can match pace with the Orks, then the Galaxy falls under the thumb of their rule in very little time. Unless the rest of the races can somehow band together or some other such heresy, there's nothing anyone could do to stop them. Keep in mind they ruled the galaxy at one time in the distant past, so it would be like getting back onto a bicycle after a hiatus for them. 

The problem with this, of course, is that we could easily be looking at Slaanesh 2.0, or something even more fucked up if the numbers get big enough fast enough.

The Eldar connection to the Warp is unlike any other race's. Where other races may feel a "connection", the Eldar are sitting in it waist-deep. They are an inherently and abundantly emotional race, so unless they can figure out how to rein in their emotional tendencies, we're going to see, at the VERY least, a recreation of the cataclysm that caused Slaanesh's birth. Whether this just mega-boosts Slaanesh, creates an entirely new entity, or even does something totally different, nobody could say, but chances are good that whatever happens might tip the scales in Chaos' favor too far to be balanced again.