Cracked Dottore Theory after AQ Act X
So before 6.6, theory crafters, like catwithbluehat, were talking about the possibility that Moontore opened the false sky so that he could extract forbidden knowledge to use against the Irminsul tree. Correct me if I am wrong, but I am pretty sure forbidden knowledge/ abyss was not used to describe the Irminsul corruption; it was instead described as Moonottore infiltrating Irminsul via death and corrupting it by trying to change fate.
So here is why I think Moontorre actually opened the false sky in 6.3. Dottore's main goal has always been to be free from the world's fate, and the best way to do that is by becoming a Descender. The only Descender that we know of that originated from Teyvat was Nibelung, but he first had to leave Teyvat. Also, in the latest AQ, Datatorre mentions how his soul was split in two, with one being sent to Nod-Krai and the other being locked up in Northland Bank. From the AQ we know that Moontorre and Datatorre are the same soul of Dottore (since Moontore perished to enter the leylines). What if this other soul was then sent through the opened rift to go outside of Teyvat? Alice mentioned how costly it was interms of energy to open a rift like that, so his usurping of the Moon marrows for this purpose would make complete sense.
Finally, Dottore at the end mentions how he is satisfied with the end he got (burning of Irminsul). This could mean that this was his plan all along, to sacrifice the Omega segment so that another part of Dottore could escape Teyvat for the time being, and also destroy one of the core things the HP uses to bind people within their fate.