Well others have already posted about this but no its already confirmed by Yoshida that FF14 is its own universe. Technically they could rewrite this later if they feel like it..which I hope they never do. Also the shards simply cant be other FF worlds because we know what happens in the first and last shard. I mean the last one (13th) was turned into the void but we know from FF13 that this ends differently (also there was no mention of Echo and the Ascians in FF13).

In the end we know that we have the source world and 13 shards but we already have FF15. Thus more games than shards available.