I like fooling around with metamagic, and am looking for a PrC that specializes in it. Incantrix is an obvious choice, but I'm (rightfully) concerned that the DM will not allow it because it's overpowered.
Solution #1 -- find another PrC that is metamagic focused. (This is a wizard.) Sadly, the only one I can think of is priestly and gives metamagic in lieu of spellcasting.
Solution #2 -- write down the Incantrix to a more reasonable level.
My thoughts on this edit are based on the following assumptions:
1. PrCs are meant to be a rise in power. Even if one is becoming more specialized, one will then act in a manner that makes that specialization relevant.
2. Classes that are "dipping-classes" have a great ability too soon and should be evened out. I would not do this for non-casters, since they need the help, but certainly for casters.
3. Drawing on #2, above, I see lots of builds that take Incantrix to level 3 and stop. A lot of focus should be on the level 3 ability to apply metamagics via a skill roll.
Some options for hampering that level 3 ability. These are not mutually exclusive.
1. Extend casting times to 1 round per level of metamagic being applied.
2. Reduce caster level by 1 per level of metamagic being applied. (easier to dispel and lesser effect)
3. In addition to the spellcraft roll, require a Knowledge check at the same DC (arcana or, if applying to the party cleric's casting, religion [nature for druid]).
On the ability to add metamagic on the fly (the level 5 ability), I think that the restriction that the total spell level cannot be higher than you can cast is enough a restriction -- the "sudden" metamagic feats are better in that respect. I think the ability is a little silly as written, though. It's the same uses per day if you use it to extend as it is to quicken or persist. I'd replace it with (incantrix level + Int bonus) extra spell levels per day to power metamagic on the fly.
On the capstone ability to lower all metamagic costs by 1 (to a limit of 1), that's an epic feat. This (to me) is what I really want a metamagic-focused PrC to do, but it is powerful. How about if it simply opened that Epic feat as available to the character (just like fighter 4 opens weapon specialization)?
With those changes, would incantrix be in-line (power level) with other wizardly PrCs?