The way everyone is asking about them it seems like SM already announced a debut and cancelled it ( and that is not the case). SM cant even take care of the artists they have now and it seems people want them to debut more. Right now SM has so many artists compared to other companies( 5 boy groups and 3 GGs). Members of groups that are inactive are active as individuals. Also, it seems everyone has forgotten a new SM group debuted this year(WayV). With this many individual activities and group activities SM is already incapable of handling the schedules everything is just messy and people want them to debut more groups. They have to figure everything out now before debuting a new group. It is better to take their time because a group is an investment. Red Velvet is 5 this year and that is the same difference between the years F(x) and RV debuted.
SNSD was still dominating up thru 2014 when RV debut, and was impactful in 2015 during rv's icc and DD periods with Party and Lionheart.
that allowed them to go longer, but 2016 changed everything. OOTN was and is niche popular but the gp has never cared. 5 acts(t,bp, gfriend, bol 4, MMM and to some extent IOI but that is more a a paradigm change) blew up in 2016 and RV went backwards. RR acted as a brake to that and the other R's got things moving positively.
Now with reality groups grabbing up kids, and with out a clear plan even if they have one, It looks like SM is lost in the woods. Now they are masters at coming out of that we will just have to see.