New Burst Mage Theory
OK, so we know that the new champion is female, is bubbles-related, is nice, light-hearted, and bubbly (hehe), and has a sleep CC. It's been heavily theorized that the new champ is from Targon, and there is evidence to back it up.
But, all of the Targon champions' bios have been super dark or super tragic. Even the indisputably good ones like Leona and Taric had to go through a lot to get to that point. So how would another Targonian vessel fit in with the rest?
The answer to that, I think, is that it's not another Targonian vessel. I think that the new champion is an ACTUAL ASPECT in physical form.
We know that the Aspects, sometimes called celestials, reside on top of Targon and sometimes imbue humans who reach the summit with magical powers via some form of soul-bonding. We know that the celestials often wander down from Targon, lost and confused; some of them mindlessly kill civilians, while others do nothing, like the golden boy in Leona's story.
I'm hoping that the new champion sheds light on the Aspects themselves and their spacefaring empire, as well as their motivations. They are currently just a huge mystery, and I'm starved for new lore on them.
Also, the champions released or VGU'd this year have shed light on certain species. Xayah and Rakan established the vastaya, Kayn cleared up the Darkin, Evelynn defined demons, and Ornn showed us demigods. I don't think it would be implausible for the new champion (who will likely be released in Preseason) to be a celestial from Targon's summit.