Such as https://www.curseforge.com/minecraft/mc-mods/evilcraft or Biomes o' Plenty's blood.

Personally i doubt this will be a thing that's normally on in the config, since it could throw off the balance of the mod.

I'd say it'd be on those mods (or another) to provide compatibility. I'm not sure about Evilcraft's blood, but I know BoP blood is plentiful in the right parts of the nether, and having such a potent source would pretty much render a decent chunk of Blood Magic's progression (e.g. runes of sacrifice/self-sacrifice, well of suffering, incense altar, etcetera) redundant. You could just hook up a pump, get some acceleration/capacity/displacement runes going, and make whatever you want.

"That isn't blood, it would have coagulated by now... don't ask how I know this."
The book seems to indicate it ain't exactly the same thing as life essence.

I echo Wrince's opinion on this. Know how Lava is super easy to get? That's just what will happen with LP if there was a 1:1 compatability.

Yeah, that was something I put in. To my mind, the act of spilling blood into the altar with the sacrificial dagger (amongst other methods) converts it into Life Essence, refining and purifying it into a usable form. It's why you need the altar and the structure around it - you can't just smear gore onto a bit of stone and hope for something to happen. Similarly, the process of filtering it into the Soul Network via a Blood Orb further refines it into LP for use in rituals and such. Each step is (barring some powerful rituals) irreversible.

It might be more reasonable at a higher (configurable?) ratio, but that's a black hole of balancing issues that i wouldn't want to peer into. Is 10:1 too low? is 100:1 too high? Getting it to the point where it's sometimes a good idea and not always a good idea or never a good idea is ... shall we say, not my idea of a good time. :P

for the record- evilcraft allows 1:1 conversion of all other mod's blood to its own blood which is also 1:1 convertible to BM blood-all handled on it's end- at least this was the case in 1.7 & 1.12 - seeing as 1.16 is still in early dev im not sure if this is applicable yet but knowing evilcraft the bound blood drop is definitely going to/does exist