It seems like Star Guardians share the same universe with Project and Mecha skins
https://youtu.be/5pYznHqxkeQ?t=3m53s
Star Guardian Jinx taunts Project and Mecha skin lines, which implies they all exist in the same universe.
The only question is the state of Battlecast skins, which right now seem like the alpha series that paved the way for both PROJECT and Mecha line. But one peculiar thing remains:
#Champions can only belong to one of these groups.
Star Guardians

Mecha

PROJECT

Now, my theory here would be that other skin lines might share that universe:
Super Galaxy
(Fizz, his icon is broken on boards now)
Dark Star

Battlecast

Full Metal

I'm not so sure on Battlecast and Fullmetal, because it's an old skin line (they are confirmed to be shared as a vision of future in which Viktor and Jayce mechanize their allies), but the fact remains that none of the Battlecast/Fullmetal champions have any skins belonging to other lines. Mostly because they and Mecha are thematically pretty much the same thing.
So, we got a bunch of champions (23% of the total pool) divided into separate skin lines. What other evidence supports the theory that Star Guardian and Super Galaxy belong in the same universe?
http://i.imgur.com/83YSxNZ.jpg
#It's all anime as fuck.
Seriously. I don't think you need to even watch any single anime to realize there's something thematically coherent in the way Star Guardians and Super Galaxy skins are portrayed. And if Jinx calls out PROJECT and Mechas, it's no longer a reference to just Transformers or Pacific Rim (let's ignore these two ones were heavily anime-referenced) - we're blending several seemingly faraway concepts (robots and magic) into one reality.
Then, if you do have any anime knowledge, you begin noticing all the Madoka/Pretty Cure references in Star Guardian skin line (Sailor Moon is a reference even people who haven't seen a single anime in their life get), you realize Super Galaxy Rumble is a one big tribute to Tengen Toppa Gurren Lagann, and you notice how Mecha Malphite was supposed to be a reference to EVA (if only the skin itself was as epic as its splash).
Dark Star isn't a big skin line yet, but I'm banking on it being too thematically related to Star Guardians to not be connected in any means.
http://i.imgur.com/RtWlxSf.jpg
What's your opinion on this approach? Personally, I love it. I always like when you can match skins in your team, and I'm quite upset when a promising skin line is discontinued (like Crimson Elite was).
Also, do you have any good ideas on what champions unassigned to any of these groups yet should get a certain type of skin? And how should be this shared universe called, "superworld", "animeverse", "weebout"?