As a general, airport wide hub effect, yes there is one. It starts at i believe 2 cities served in a very... very weak form, and maxes out around 2000 airports served.
As an airline specific form, not presently. I've got half the calculation for it figured out. it needs a little more still. Multiworlds and improving edit route have taken priority over it, but i'm hoping to have it completed by the end of the age. It will likely be in the form of a specific "Hub" class of focus city, possibly even extending to a "Major Hub" status with a stronger affect.
