(wow, long post

sorry about this :\ )
Actually, I wanted to have just one (very unrealistic) big pool for everything, much like in videogames, so I thought about using your plan B in a game with my little cousins. We were playing with spellpoints (and simplified rules for just about everything), so I'd translate each ability into an equivalent spell level (like a druid gets WildShape at level 5, wich would be when a wizard gets a 3rd level spell, meaning the cost to WildShape would be 5 spell points), but I'm not sure it would have worked, balance wise. Take Smite Evil: you get it at level 1, only once, but would you allow it to cost only 1sp? really? No, I wouldnt - not like spellpoints escalate anyway. Maybe increasing the effect (ie. bonus damage) with sp or increasing the cost each time you use it during the day (1st use: 1sp, 2nd use: 3sp, 3rd use: 5sp, etc), but I can smell 'needless complication' here...
Anyway, those were spell points. A bit different than slots.
Also, some people might have a problem with plan B because of the way these new spells would interact with globes of invulnerability and dispel magic. Having the wizard necromancer BBEG dispel your undead turning? Not cool, man, not cool...
The thing should be, IMO, having pools for different sources of powers. D&D already makes distinction of divine and arcane magic, there's also spontaneous and prepared spells, and some abilities are Ex, Sp or Su. Not to mention psionics! It's a matter of figuring wich pools stack and wich pools dont.
For instance Turn Undead and other blessings that only clerics can do (I'm talking about the "class features disguised as spells" TM, that Nifft always talk about

), they are supernatural abilities, powered by the Divine. IMO, their Spellcasting should be something that they accomplish on their own - even though they ask for the spells from their patron, it's ultimatly the cleric himself who cast the magic (imagine you borrow a friend's car, then run over an innocent bystander. Who should take the blame from such "accident"? You or the owner of the car?). On the other hand, spells are not like divine abilities: the Divine CAN and WILL stop your Smite Evil against non-evil opponents (It's like you're on the passengers seat saying "could you please, run over that man").
So to me, they are different resources. Domain slots are the only spells that the Divine should have a saying on. But what makes them different then class features? I don't know... maybe they should be considered supernatural abilities and not spells per se.
Ok...
So, just for the heck of it, let's consider joining turn undead and domain spells into one big divine energy pool, with the ocasional smite evil and cure disease in the middle. The pool could be as large as your level in cleric plus Charisma modifier (I think these could stack with druid and half paladin levels, if multiclassing is available - or maybe summing up effective Cleric level for Turn Undead ability). Maybe lower/higher than that, I don't know...
Anyway, Turn Undead remains unchanged (I do want to change it though, but that's another topic), each turn attempt costs 1 channelling, or one use of that divine pool thingy. Then let's get rid of domain slots. Clerics still get 2 domains (and related powers), but We could say that each domain spell costs 1 channelling from spell levels 1-3, 2 channellings from spell level 4-6, and 3 channellings from spell levels 7-9. Every two levels the cleric gains 2 new spells (one for each domain) that he can cast using his domain slots (no need to prepare them, i guess...).
Another thing that should be in there too are spontenous cure spells. Maybe curing 1d6 per 2 cleric levels per channeling use (like 4d6 at 8th level), or maybe charging a number of channeling like in the domain spells option above for the common healing spells CLW, CMW, CSW, etc. but with 1d6 instead of d8, or increasing casting time (1 full round per spell level?) - so the Healing domain and prepared spells arent so worthless... anyway, I guess it's just a matter of personal taste here.
Finally, every spell that's pretty much divine, should get into this mess (you know, things like bless, hallow, etc... Nifft is allway talking about this), but maybe this is probably acomplished best as a list of suggestions for each DM, and should have limited or reduced effects than its prepared spell counterpart - they could be more like "long rituals with lots of chanting and acolytes" than "pull the trigger NOW, Johnny!" kinda spell.
Now, the cleric has spellcasting (wich is like a skill, something you learn and master on your own) and divine channeling 'superpowers' (wich is granted by a deity, almost wether you want it or not, say a curse/reward thing). Other classes could work the same way: druids would get Summon spells like the domains here, and wildshape costs an amount of uses from the Energy pool depending on creature size complexity... but Multiclassing will still be a bitch: A Druid/Cleric gets how many points in his pool? An orc cleric of war with levels in druid should not stack his levels, should he? But an elven nature priestess druid/cleric should, right? Not sure about anything here...
(my god, reaaly long post

sorry about that :\ )