From Reinhart's unofficial translation of the live letter:
Quote Originally Posted by Reinhart View Post
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# Q27: How will the primal fights change in ARR?
# A27: They will be basically be the same as the fights in version 1.0. However, we will be making some minor tweaks based on the new battle system and the primals will have a larger role in the main scenario.
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f; How will the primal battles such as Ifrit, Moogle, and Garuda be in ARR?
y; umm, basics for those that played previous FFXIV, just imagine the primal battles from then
y; however, this time it involves with the main scenario so the standing position and cut scene is different
y; also the skills they use is matched to the ARR’s battle so it’s different
y; Say for Titan, Titan is new, like there are many things, like the ground breaking through, flying, dropping. There are lots using ground gimmicks.
y; And as the contents gets updated, less people will play, so at that time we’ll have Ifrit show up in public field, and like the benchmark it becomes a F.A.T.E. and from there people can use it as great summon (dai-shoukan)
Sounds to me like they're going to start as instanced fights (sounds like static location rather than roaming since they may be involved in the main story, but hard to say at this point), and then later be reimplemented as FATEs or something similar. They certainly have seemed to back away a bit from making them completely roaming, but perhaps not abandoning it entirely. I think we're just gonna have to wait and see for ourselves, unfortunately.

I don't remember hearing about Odin getting stronger, though I don't doubt that the info is authentic. It worried me a bit because there's going to be hard-core groups seeking him out and defeating him constantly, quickly raising the difficulty to a point where it would be hard for less die hard groups to ever take him out even once unless there's a certain maximum he'll cap at...