We know that Pinkie is very much in love with Sunset. Whether it's a levels of obsession or just deep and true love is up to interpretation, but it's very clear that Pinkie loves her.

We also know that Sunset, although she considers her a friend, is not in love with her. Sunset is straight, or at least is hanging heavily out in 0 territory on the Kinsey scale. She admits that Pinkie embodies a lot of the qualities she'd like to see in a significant other, except that, well, she's probably missing the most important part.

Or is she?

No, I don't mean that. Get your heads out of the gutter.

What I mean is that we've mostly looked at (or have been forced to focus on, rather), Pinkie's views and Sunset's views. But we really haven't looked at the other character's views much. And if you do, what do you see there?
Twily (and arguably Tavi, Soni, Dagi and Ari as well): Don't hurt her, Pinkie; otherwise, we accept this.
Sunny's parents (on both sides): we're okay with this. Hell, Celestia is all for it, apparently.
Applejack: no real comment
Rainbow: jokes aside, no real comment
Fluttershy: leaning towards Pinkie/Sunny
Rarity: Do you really need to ask?
Mane 6: Pinkie already thinks of them as a couple. The others either don't know or don't have a position.
Shimmer (Sunset's "twin"): is okay with this.
Compass Rose: Well....

And let us not forget Sunny's own words to Pinkie: that she knows what Pinkie is and it comforts her and scares her at the same time. Why would that be?

The point I'm trying to make is tied to that old saying, "people know you better than you know yourself." It's pretty clear: Sunny and Pinkie are meant to be together. Sunny either just doesn't want to admit it consciously (even if her subconscious knows), or she's trying to fight against fate (which is typical for her). But even still, it's clear that she loves Pinkie as well, and in that way...she just can't bring herself to admit it in a conscious way.

It even took Pinkie a while herself, as shown by the events of Downtempo. But it will happen.

Oh and the alternate reality with the SunPie pairing? Clearly a red herring.

6951986 Hmmm, good points, these, and much food for thought going forward.

Well, It's an interesting theory, but you guys are forgetting one important thing: both Sunset and Pinkie have had bad with a capital BAD relationships that they're both coming off of and they're reacting in two individual ways (which is natural):

- Pinkie is looking at Sunset as her ideal. Maybe even as her idealized self, what Pinkie really wants to be: beautiful, smart, mature. Pinkie has, in her mind, maturity issues (even if others, such as Twilight, don't agree). She's clearly beautiful, but she doesn't feel that she is either. In many ways, Pinkie is like Fluttershy used to be, but doesn't show it as much.

- On the other hand, Sunset looks at Pinkie as having the ideal qualities of a boyfriend: cute, funny, charming and friendly. Stuff that we know that Flash doesn't have. It's clear that she wants someone like that in her life. But that doesn't necessarily mean Pinkie.

And there's the particular immortality issue as well. Sunset's a goddess. Everyone else isn't. How do you square that?

6952202 Hmmm, good points there, Shin.

And there's the particular immortality issue as well. Sunset's a goddess. Everyone else isn't. How do you square that?

Again, good point, and not easily or well, I'm thinking.