1) It's FFXIV, not FFIV. FFIV has already been released. With a remake, even.
2) FFXIV is not related to FFXI. If you read the interviews, you'd know that.
3) SE plans to keep making content for FFXI so long as there's a playerbase to make the content for. Odds are a lot of people are going to prefer staying in FFXI for various reasons, so there will still be a playerbase even if it does dwindle a lot. Keep in mind there are many servers that can be merged together, so you wouldn't notice the difference at all. Everyone thought WoW would kill FFXI, and it didn't. Everyone thought Warhammer would kill FFXI, and it didn't. FFXIV will have an impact on FFXI, sure, but FFXI has peaked already, so its definitely not too early for FFXIV's release.
R.I.P Teraud, Dragoon main on Seraph (2004-2007)
R.I.P. Atli, Blue Mage main on Seraph (2007-2008)
R.I.P. Silje, Beastmaster main on Odin (2008-2008)
R.I.P. My Final Fantasy XI Account forevahz
Back on ZAM for FFXIV!