Involve me doing Discerning The Transmundane?
I finished the Soul Cairn quests, culminating in receiving the Blood Scroll, but when I went to the College to ask about the other Scroll, I ended up doing this quest!

*facepalms*

You sir just failed for some reason.

I believe so

How did I "fail?"
By doing something that I have no control over?

This doesn't have any effect on the main quest does it?

No. I've gotten the scroll early plenty of times. It simply means you can use the scroll immediately.

Thanks for the info. Just worried because I'm avoiding the MQ on my current character.

You failed to realize that it does not really have anything to do on the main quest.

Seeing as how you have to do the exact same quest to acquire the elder scroll to learn Dragonrend, fulfilling the exact same requirements, and there's never been another instance, until now, where you've had to do the same things, how would it not have anything to do with the Main Quest?
You tried to be funny...and it didn't work. Instead, you displayed a disheartening lack of intelligence.
I salute you.

You were asking about the vampire quest, I doubt it in any way relates to the vanilla main quest at all.

Blood scroll, as you refer to it, is not the same scroll you get in the MQ

In the MQ, you get the Blackreach scroll

Blackreach scroll is involved in 2 quests: MQ, and Discerning the Transmundane

You can get the Blackreach scroll when you like. You can use it in the MQ if you do the MQ, but DtT is a daedric quest completely unrelated.