My issue with that, is when it comes to buying ships. I just bought two Dag'Kar's for use as allies in an upcoming Battle 5 campaign. So as we redefine what is and is not an ally, the minis I bought are no longer legal.
So from a new player perspective, pulling miniatures out of my fleet, and telling me I can no longer use what I purchased, is obnoxious.
As I understand the early days of the Interstellar Alliance, the Narn's were enlisted by G'Kar to bollster the security forces of Babylon 5. When my local group recomended the Dag'Kar I jumped at the option as it allowed me to represent the Narn's support of Sheridan, in exchange for his help in freeing the Narn Homeworld. That support for Sheridan would not soon be forgotten.
If all else fails, you could always build a Narn fleet... damn the luck ;>
Also - E Mines are neat =)
So would I want Centauri allies? Of course not. Earth Alliance, Narn, and Minbari ships all aided the White Star Fleet at one time or another, and some smattering of League craft as well. I would support a restricted list, maybe nothing above Raid priority, or something similar. You're not likely to find a fleet of Q'Quon cruisers, but a handful of fighters, or smaller craft (did I mention I really like my E Mines?) would make sense.