We are already 15 months and no announcement, Orange as a studio is... kinda weird compared to conventional studios, because since before their conception, the idea was to make good CGI, as stated by it's founder, and the majority of the staff are talented CGI artists the founder have worked throughout the years.
Because of this, the studio is small as hell and work mainly in collaboration with other studios to do the CGI parts, as they specialized in that.
With that said, as a small studio, they cannot have too much work at once or they quality faulters and lose their status as good CGI studio, so, if they are actually working in a S2 for Houseki, not only they would have announced it inmediately, because they need every bit of publicity they can have, and also they are still small to do series on their own (they have only Houseki and a Monster Strike movie under their belt)
I belive we will have that S2... but maybe in 2021 o 2022, probably when the manga is in it's final stages or finished if the 108 chapter theory is true
. So go read it now, unless you want to wait 5 more years.PRAISE ICHIKAWA