Doctor MEI is in love with the strongest character in Honkai lore currently, Kevin Kaslana
They were in love with each other, which was tragic because after becoming MANTIS to help MEI with her research, his body temperature dropped too low for him to be around people safely ever again, so they never even embraced ever again afterwards; they also had a son together, but not through conventional means obviously.
I think the project ark stuff is less likely, because iirc the official status of that project is "failed", since they lost contact with it.
Project valuka and project ember are more interesting to me with how they could tie to the honkai lore.
Project ember because its failure showed that sudden advancement of tech just makes honkai more dangerous faster and destroy everything.
This to me sounds like what happened to khaenri'ah, heck dainsleif's "curse" of immortality just sounds like a stigmata effect.
It sounds to me something like project ember happened in khaenri'ah (perhaps as the result of project ark?), which caused a will of honkai reaction, which caused the people to develop stigmata; some mutating into what's now the abyss order, and some being naturally compatible like dainslef.
The reason why I think project ark itself is less likely, is because project valuka is currently also "failed", and the entire goal of project valuka was to find worlds on the imaginary tree where the honkai was defeated, but we also know that otto saw dvalinn through the imaginary tree.
So that could mean three things:
1. project ark is connected to genshin, making the actual genshin world actually present somewhere in the main universe, which means the dvalinn otto saw was an alternate genshin world/bubble universe/whatever; project ark causes project ember like behaviour in khaenri'ah.
2. project ark has failed and the genshin world sits somewhere on the imaginary tree with its own expression of the will of honkai
3. "the stars are fake" and the genshin world is just data/sim retreived by project ark, this also means the dvalinn otto saw was an alternate.