Q u o t e:
How will the new expansion effect FF mages?

The intent is that for fire mages that emphasize the mastery stat, frostfire bolt with glyph becomes a better option than fireball with glyph (and yes it's a temporary aberration that scorch is better than fireball).

Q u o t e:
As most are now realising, I think Kalgan meant that Frostfire Bolt glyph would replace the Fireball glyph, not replacing it in the rotation.

No, I actually did mean we intend players that glyph ffb to replace fireball with ffb in their rotation entirely (we're trying to avoid over-complicating the rotation). The current tuning for ffb, glyph, and mastery obviously don't get it there, but those can change (along with other stuff, like making the ffb dot stack).

Obviously, it's still complex to resolve scaling, etc.