What's incredible about the Unfriended rumor is that isn't even seen as a viable franchise in the eyes of Universal. The sequel (Dark Web) is being released through BH Tilt, Blumhouse's in-house distributor, used for smaller, targeted films that Universal (or other major studios) pass on. That says to me that Universal felt Dark Web was A) bad, B) too intense/problematic in content, or C) a little of both; it's not like the first one wasn't a huge financial success.
Now, it's unclear if this rumored component of HOBv2 will feature the first installment (which was a Universal film), the second (which isn't), or both (not impossible - see Sinister). The first-only would make more sense/avoid the seriously-unpleasant-can't-emphasize-this-enough human trafficking element and would focus on a Universal film, but it still feels weird that they'd want to bother synergizing with a franchise they're no longer spearheading.
Most baffling of all, by the time the maze debuts in September, the theoretical promotional window for either film will be long gone. Truth or Dare debuts on home video this week, while Unfriended will enter and leave theaters before August even begins; a home video release is possible for October (considering BH is handling distribution themselves), but it's not like they're going to be leveraging anything substantial here.