I actually really, really like Morgana x Varus. x: Both looked into a dark power to do what they felt needed to be done. While Morgana is painted as the 'evil sister,' Kayle might not actually be so good herself - it's arguable that Kayle was quite tyrannical, and in order to fight back that threat, Morgana looked into the 'dark arts' to be able to fight back. ("One side proclaimed themselves as beings of perfect order and justice, fighting to unite the world under their law and strong central governance. Those that fought against them saw their kin as tyrants, creatures incapable of seeing the larger view, who would sacrifice individuality and freedom for the illusion of efficiency and safety")
Varus had done a similar thing. Together, they both became "corrupted" for what they both felt was the better good.
I think they both also actually deal with some kind of physical pain due to their powers too. Varus has to worry about being consumed by his corruption, and Morgana appears to have lost the ability to fly outright with tattered wings, etc. Morgana, being a mistress of the dark arts, could also possibly look into some kind of means to also halt the progress of Varus' corruption, too.
Morgana and Varus are probably, to some degree, 'out of their element' culturally, too. Morgana comes from another plane of existence, and I imagine to some degree Varus would have some culture shock...? Birds of a similar feather to some degree, I suppose.
I guess I like it for similar reasons as you like Soraka x Varus, so I thought I'd share. xD It's a bit more of a darker equivalent, though.
I've never really thought of a pairing of anyone with Soraka though, even though Soraka is one of my favorite champions. I guess I just don't really ship a lot of things in league, lol. (mainly just morgana/varus, syndra/zed and lulu/veigar I guess)
I've thought of Soraka/Irelia because I think Soraka saving Irelia from death (and then Irelia coming back with her newfound powers) could be cute but I guess that's about the farthest I've went with that idea. xD
That said I could get behind SorakaxVarus too though. c:
Though I just saw this and I'd totally support this as a ship if we had a blacksmith character though, lmao
http://img11.deviantart.net/8b45/i/2015/114/a/f/single_celestial_female_seeks_blacksmith____by_busubusu-d5gkiwu.jpg
or 
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