Must be frustrating for dramas to do this all the time, but on September 13, MBC stepped up to address the reports that got ahead of themselves by claiming so-and-so were confirmed to act in the series.
A rep of the drama 'Illumination' made it clear that nobody was confirmed for a part by stating, "Jin Goo, Lee Yo Won, and UEE are not confirmed for appearances. There's not a single actor who is confirmed."
However, more confusion arises from the fact that BH Entertainment announced the same day that Jin Goo was confirmed for the drama. Apparently, he is confirmed while Lee Yo Won and UEE are up in the air.
Either way, the drama will air sometime in November.