I don't like ninjas, samurais and Vikings, but they are already in.
Also, where do you see Conquistadores and Persians?
Persians : sarranid stuff
Conquistadores : morion and side sword
Even more, some ppl are multi-style : samurai armor with nordic helmet, shield and axe...
Tbh, i don't really like roman style and if implemented i will ot wear roman armor, but it will not change the general ambiance, it will just add new choice and new style.
In SP, you could find the samurai armor (strange armor) in garbage in a town, meaning samurai could be a civilization from accross the sea, i don't see a problem if a roman civilization could come from another place (the Calradia map don't end at east and south, there is place for new civilization).
You can argue that we can add firearms too, but firearms have some effect on game mechanics (and whine : more ranged!) new models of armors will change nothing to game mechanics (and at least we could see proper hoplite!).