candleanfeather posted some thoughts on foreshadowing of Spike and Angel in S8, and this prompted me to re-read 'Always Darkest'. And you know, in light of what we now know about Angel, Twilight, and shiny glowing auras, 'Always Darkest' really is absolutely full of foreshadowing:
1. The first thing Caleb says to Buffy is "It's the one lesson you always forget, girl: you can't kill what's inside you." And now we've learned that Buffy apparently has a sparkly glowing force inside her that wants to connect to that other person glowing with "unholy power".
And meanwhile, Giles says "Regardless of what Buffy does, there is no winning", while Angel says "She's about to face something she truly can't fight." It all seems to be setting up the glowy force as an enemy, and one that Buffy won't be able to defeat through brute strength.
2. Buffy sees Spike and Angel, and rushes towards them - but toward them both equally, and Spike jokes to Angel "She can't even tell us apart." This is just speculation, but now I'm wondering if the prophecy or whatever that Angel thinks connects him eternally to Buffy could also apply equally to Spike - since they're both vampires with souls, and maybe the ancient mystical forces, like Buffy, "can't even tell us apart". So maybe Spike's upcoming appearance in S8 will be key to finally defeating the glowy force? (Compare Buffy substituting herself for Dawn in 'The Gift', though hopefully the finale of Season 8 won't be quite so fatal to those involved.)
3. Angel replies to Spike that the reason she can't tell them apart is because of "the outfits". That's a pretty clear reference to his Twilight outfit that prevented Buffy from recognising him.
4. I suspect the spangel sex scene was just Buffy's libido at work within the dream, though it confirms that she's still sexually attracted to both vampires with souls.
5. The story ends with Buffy marrying skinless Warren. On one level, this could be simple foreshadowing of his (supposed) switch of sides to ally with her. On the other hand, in her dream Buffy is marrying a misogynistic murderer who killed her friends... foreshadowing for what she's doing at the end of 8.33?
If the direct analogy that Angel=Warren is a bit too radical, perhaps the dream's intended warning is rather that it shows Buffy a scene of her being so overcome by love and passion that she is happy to marry a disgusting slimy monster... and this is supposed to alert her that her waking-world feelings now are likewise being manipulated into doing something equally unwise with Angel.
So... if 'Always Darkest' really was a prophetic Slayer dream, it was warning Buffy that something 'unkillable' inside her will fool her into thinking she wants to marry one of her worst enemies. What could that possibly be referring to? ;-)