ESO is build to be a Massively Multiplayer Online game (MMO) , not just a Multiplayer Online Game, which seldom accommodates more than 64 players per map (= instanced "server"). The server-side infrastructure is hugely different; MOGs like Battlefield cannot handle thousands of concurrent players in the same world, nor would it make sense for them to do so -- MMOs are not meant to be compartmentalized, they are intended to live up to the "massively" part of their name.

So, don't expect to see anything like this. Btw: the term "private server" in the context of MMOs means running a (reverse-engineered) software which, more or less badly, emulates official servers. This is of course highly illegal, not just by the Terms of Service of the MMO's provider, but by the DMCA as well. (Disclaimer: I'm not a lawyer, and the former should not be understood as legal advice.)