Nationalism as in nation-state dates back to 323 BC? I would be surprised. I think historian debate if nationalism was born in the 17th or the 18th century, so maybe they are all wrong, but considering how many new, interesting debate are indroduced by Chinese historians (== academics), i doubt the debate wouldn't already have fired if this was a question.

At the time, ruling over different culture and languages was a sign of power. Chandragupta's empire included Bengali and people from Deccan, and i think it extended beyond the hindus (Sorry if it the the english term, i'm not fluent enough to read history books in english). I would be VERY surprised if any of those considered themselves as Indian before anything else.