I've been hearing a lot that the Unknown IP could be Blumhouse and with recent rumors FNF may not be coming it'll be Megan paired with Imaginary. Though Lionsgate acquired the full rights in 2023 to Imaginary and most Blumhouse houses at HHN were distributed by Universal and Imaginary wasn't. This doesn't eliminate its chances but I'm doubtful Imaginary would be coming.
While it's not impossible that they could work with Lionsgate--I also think when you consider the upcoming release schedule of Blumhouse (and Atomic Monster--feel everyone needs to consider that now too with AM out of WB jail) that there is really a whole lot of nothing that could make sense.
Even going back to older catalogue; better to use them for smaller purposes like meet & greets for Behind The Screams at Hollywood (or RIP for Hollywood) or the Peacock Bar for Orlando.