So a couple of days ago we got more news concerning the mana regeneration changes. It still seems like Intellect gain ground over Spirit, but not being a number cruncher I must confess it is only a guess from my part. Basically we will get a 40% reduction when OO5SR and regeneration while casting is said to be more or less untouched.
Apart from Innervate that is sprit-based, many of the other mana regeneration spells are based on the maximum mana pool, i.e. based on Intellect (e.g Hymn of Hope (even Priests own Holy spell is Intellect based), Mana Tide Totem, Replenishment).