As far as I know, Bae Jungnam resumes appearing on My Little old Boy as a cast member from Ep 406. As he gains quite a lot of support from the mom’s in the studio but also from those who watched the TV show.
Given the success of Our Unwritten Seoul (미지의서울), I hope there’s a possibility of a spinoff of the series (Our Unwritten Seoul) where it could be film at different metropolitan cities in South Korea. To become a franchise called Our Unwritten Series.
I do think that the third season may have hints that Jo Jung suk Hyung’s cameo appearance in the last episode of weak hero class 2 maybe related to oh Jin won (whom is played by Jo Han-chul) because of his abuse of power as a cruel assembly man which may have links to Cheongang although the character did not appear in the sequel. (Weak Hero Class 2)
This drama from what I know from my POV, is an answer to what took place after the events of Who are You: School 2015 although both dramas are completely different, having different storylines, characters & the stars who star in the drama.