My apologies . I read the header and assumed it was replacing the current rules for dealing with spellbooks. I should have asked that instead of jumping to conclusions.
[edit] Just got back into town. I had thought the header matched with the section from the playtest document, but now that I have my copy in front of me I noticed that it only roughly matches one small portion of the spellbook section.
Do you mind if I ask whether it will be replacing the section for casting directly out of a spellbook (labled "CASTING SPELLS FROM SPELLBOOKS" on page 116, the section I mistook it with) or would it be in addition to them? I know you said it wouldn't be removing anything, but I want to make sure I've got the full story this time. Now that I can read through them together and compare them I realize there's only a few changes:
1) Use INT to determine max mp instead of it not being capped.
2) Much easier INT checks
3) Longer casting time
4) Always a health cost in place of MP (and Health if you fail badly).
Now that I've taken the time to read it I don't think it would be a *huge* loss even if it did replace "CASTING SPELLS FROM SPELLBOOKS", as long as the section on prepared spells sticks around. I like the current rules, but I can see why they might get dropped in favor of a simpler system.
The way I see it though follows (correct me if I'm wrong):
1) If it replaces the current "CASTING SPELLS FROM SPELLBOOKS" section and preparing spells remains there'd be very little point in primary casters using the system (any spells they could cast with this they could just prepare anyways), assuming their magic stat is higher than or equal to their INT. It would be significantly cheaper than this option, and although it pre-allocates some MP it would be much more viable at a moment of need. I could see them using this is for low-mp out of combat spells, but I haven't had too much of that come up in the couple playtests we ran.
2) If it augments the current system the above applies, so primary casters likely wouldn't use it, but they have the other method to go by which would be of great use when trying to cast a powerful spell they normally couldn't.
1 & 2) It introduces an interesting new system for secondary casters and non-casters who have little or no MAGIC stat but a lot of INT.
I apologize again for my confusion earlier. If it's not removing options elsewhere I can never object to adding in more options xD