The thing about Agni is that the guy whose 'baby' she was left Square last year, and really wasn't with the company very long at all - he joined them from SEGA (where he lead designed their gorgeous 'Hedgehog Engine' that powered Sonic Generations etc), did work on Luminous, and Agni as a part of that, and then left. He left (a real blow to Square) immediately after Square shut down a bunch of projects because money was tight and took a bunch of his team with him, so I've been assuming that whatever he had campaigned hard to move on to after completing the Agni demo was one of the five or six early-stage projects that got canned. Some of them would've been canned naturally, of course - SE does speculative early development, so they might early-dev 5 projects but only 2 will make it to full dev anyway.
The Christmas card featuring Agni, however, came after he and pretty much most of his team left, so who knows?
That aside, I think there's a pretty strong chance, given the Nomura situation, that Naora (the Agni card) or Yoshida (FFT/12/14) will be the art lead for FF16 anyway.
RE Eidos: The thing is, Eidos' teams are arguably too busy to work on such a game. Deus Ex, Tomb Raider and Hitman are all running at full tilt right now. I expect more Western influence - because they've been hiring a lot of Westerners over into FF15 in an attempt to diversify - but I don't expect a fully-Western developed FF any time soon. I can see them assisting Japan, but the smartest way to do that would probably be to set up a small studio for that specific purpose, like Sakaguchi and the Hawaii office for FF9. FF9's refreshing European-style of fantasy really came from the fact that the lion's share of its CG artists were Westerners, even though the concept art was coming from Japan. It made for an interesting mingling.
As far as FF16 goes, I increasingly think people should also consider outside the typical names, outside the box. What if it's somebody new to FF from a high-level position?