Well, what I was thinking about was:
Feel free to critique, but anything completely unreasonable or broken is due to all this being a stream of consciousness, not out of a desire to sneak something through.

This is all subject to change.

Origins as Innocent (drop-in), Witch, Whitelighter, and Demon (which costs more but comes with a free, exclusive perk).

Innocent would get a perk that lets them ignore and stay out of the "plot" of settings if they don't purposely get involved in it, detective skills, and maybe something that makes them really clever about exploiting loopholes in magical going-ons.  The stupid, but I think kind of fun, idea was to call their capstone Supernatural, which just makes them really, really good at fighting demons through mundane methods.

Witches would probably get a snark perk, a rhyming perk, and a "Family Emergency" perk that gives you a knack for slipping out to deal with extraordinary problems.  Not sure about the capstone, maybe something about working well in a group to bring out true power.

Whitelighter gets perks to help them with being the white mage, probably emotional support stuff or stuff related to not being the focus in a fight.  Also, a 1-up perk as their capstone, representing how they're already dead, that can be bypassed by stuff designed to kill angels.

Also, as a special mechanic that I imagine will leads to some complaints, since they can only be killed in universe by a few things, Whitelighters can choose whether they benefit from the "can't die 'cause they're already dead" thing, but Darklighter poison will no-sell defensive perks from other settings, or whether death counts as normal but other perks are in full effect.

Demons get a free perk that gives them a capacity to shrug off mundane stuff like handguns, but as a tradeoff they cost a little more than other origins.  Probably perks based around developing connections in important positions, maintaining control by occasionally executing subordinates, and, this is just an idea, the ability to resist esoteric effects by the simple virtue of being much stronger than whatever's trying to affect you.  In RPG terms, someone 50 levels lower than you wouldn't be able to turn you into a frog, but their fireballs and swords would hurt just as much as normal.

Undiscounted perks, maybe spread around if I can't think of anything better, would be stuff like being pretty, having your actions count for your alignment more than what types of powers you use, and a "dead bodies disappear" perk, based on how demons were nice enough to just disappear and not make our heroes have to hide their corpses.

There'd be a magic section where the rules of magic are explained and Demons and Witches get to pick their "instant cast" power from two separate lists, as well as a note on how they can expect their power to grow.  I don't think they ever explained how demonic powers develop, so I'll probably just say that Witch powers tend to grow mainly in breadth, though they do get stronger, while demon powers grow more in depth, though they do get more versatile.  Whitelighters just get the standard Whitelighter powerset, which would suck if it wasn't a really good support set.  Innocents might need a little something here to compensate them for no inherent magic, maybe letting them buy another origin's magic or giving them a stipend to spend on items?

There'd be a magic booster option too, which does different things depending on your origin.

Innocents get Slayer, if I decide to go through with making their Capstone Supernatural, which basically turns them into Buffy.  Taking both is obviously very effective.

Witches get to come from a strong bloodline, which gives them a bunch of ancestral ghost witches they can ask for advice, plus overall stronger magic.

Whitelighters become Elders, which gives them a Wisdom boost, Sith Lightning, and Angel-based respect in other settings.

Demons become "The Demon of X," which leads to a huge power boost and additional abilities that depend on what X is.  I'd probably do another list instead of a "fill in the blank" option, just because I have a personal preference for those.

Maybe a Hybrid option too if I can think of a combination for every origin, but you wouldn't be able to take that and the booster, because it'd be too much work to figure out what a boosted hybrid would do.

Items

Innocents get detective gear, munitions, and other stuff.

Witches get a Book of Shadows containing the sum total of their magic knowledge, and the knowledge of their ancestors too it they took the booster, and a turnkey business that follows between jumps.  Maybe a house too.

Whitelighters get Memory Dust, and I don't know what else.

Demons get dosh, and other stuff.

Companions

Innocents get a normal, but skilled, person who suspects that there may be something hiding in this world's shadows.

Witches get a Whitelighter companion.

Whitelighters get a Witch Companion.

Demons get a demonic Seer, who the fluff says has somehow managed to glimpse that you're not of this world and have a generic and indeterminate "great destiny," and so has become obsessed with serving you.

Drawbacks
A "The Big Boob Incident" 100 CP drawback, where you experience an embarrassing magical snafu early on, and your allies never let you live it down.

A drawback where, during fights, you and your opponents keep getting flung around across the room and breaking all your stuff.

A more expensive "No Personal Gain" drawback where the use of any supernatural powers for selfish reasons, even ones from other jumps and even if you're a demon, cause you to experience unreasonably strong bad karma.

A "The power of 3-6-9" which increases in severity and points awards the higher up the tiers you go, and which requires you have at least 2-5-8 companions.  All of the powers of everyone affected are reduced to 1/3, 1/6, or 1/9 their normal level, depending on the tier, and only by performing a short ritual can you temporarily restore them to full strength.

A capstone drawback where its prison is destroyed and the Hollow starts possessing people and demons to hunt you down.  Despite what you might expect, it is not immune to powers from other settings.  In fact, even weak ones are utterly devastating to it because it doesn't posses any natural resistances to their metaphysics.  However, every time you kill its host, the Hollow will escape, stealing whatever power you used to kill it in the process.  At first, it will posses only a rudimentary, instinctual intelligence that is incapable of any strategy besides a suicide rush, but it will slowly learn as it continues to fail and die.  The only way to stop it is to figure out how they built its prison the first time, and trap it again.