Carrying capacity refers to an environment’s ability to support a population, or varied populations.
For EVE that means players. But we have different types of players. Broadly defined as PvE and PvP, and then also as paying and non-paying.
Here is a game that shows rabbits and wolves and grass in various examples of how different variables can effect carrying capacity…
http://www.shodor.org/interactivate/activities/RabbitsAndWolves/
What that means for EVE is various.
Does EVE need empty space?
Does it need more rabbits or more wolves?
How much elbow room do players need?
Et cetera
Personally, given the amount of time that EVE has been around, and the energy and intelligence of the various people who have been in charge of EVE’s growth and development, EVE has reached its maximum carrying capacity.
Not that the population remains the same, but that when an influx occurs then others leave as the space gets too crowded. For example, it’s nice Jita is a busy hub, but would you like every hub to be that crowded? Every mining spot? Every mission area?
Growth can kill.
Which means ongoing success relies on how to increase revenue from existing players, or creating another space in EVE’s space where growth can occur.