United States Census Bureau puts Earths population as 6,895,600,000
The CIA World Factbook puts the growth rate at 1.13% and the US population growth at 0.98%
Gallenteans began colonizing beyond their own system around 750 years before the capsuleer era.
Assuming a population equal to Earths then:
750 years at world growth = 31.5 trillion
750 years at US growth = 10.4 trillion
(Note: I'm not great at math. If these numbers, or any others, are way off please correct me.)
Of course Gallente Prime is not Earth, the Gallente had likely started expanding into their home system already, and growth rates go up when prosperity, space, and resources increase. Given the many unknown factors I wouldn't say 2.8 trillion voters is unreasonable. Even if the number was made up on the spot with little thought it's not necessarily a "bad" number.
Add in three more empires and a variety of bloodlines along with the period of great expansion for the Amarrians and a number of bloodlines being consumed by the Empire along the way during over 2000 years of colonization and I wouldn't call values in the tens of trillions extremely nonsensical.
In addition it's surprising to me that someone would call 2048 years, or even 750 years, relatively recently. Especially in relation to a compound growth rate.
Of course human history to this point is a poor measure of the nature of populations existing in an environment of inter-planetary colonization with vastly more powerful governments able to engage not only in colonization efforts but the terraforming of new worlds along with automated farming, nano-technology, underwater cities and non-planetary colonies, mass breeding of slaves, and perhaps most pertinent to this discussion improved medical science and lifetimes that can extend far beyond our own.
While the hazards of New Eden may keep the mortality rates high in certain areas I'd say these factors justify a guess that places the population between the exceptionally wide and forgiving goal posts of tens of trillions.
Ref:
http://wiki.eveonline.com/en/wiki/Timeline#Age_of_Expansion_.28AD_16262_-_YC_100.29http://en.wikipedia.org/wiki/World_populationhttp://en.wikipedia.org/wiki/List_of_countries_by_population_growth_rate