I searched and did not see any recent topics concerning the origin of the nucleus. I have read books that suggest the nucleus may have arose in eukaryotic cells as endosymbionts. When I speculate at how the nucleus might have otherwise originated (internal pinching off of lipid membrane) I have a hard time seeing which one would have been more likely. If anyone has any research on this or interesting insight I will definitely give a read.
Raven’s Biology briefly mentions that the nucleus may have originated from an archaean. Some archaea have histones and similar DNA-processing enzymes, which supports this hypothesis. I haven’t seen too much research on this, though.