It was during a C2E2 2017: Marvel's RESURRXION Panel if I remember wright. The one where we could had a glimpse on the X-Men Blue covers #8 & 9, thus learning the return of Emma Frost and Polaris
I remember the pictures were took on the screen like this one
Probably information from Cullen Bun
Both Newsarama and Comic Book Resources had relayed the same information
Does it ring a bell to someone please ?
Seems like what we got during Secret Empire was what they meant:
"The crossover issues will feature the return of the Hellions and the gun-armed mutant known as Random, but the characters fans would be more interested to hear about returning arrive in issues #8 and 9. That is where fans will see both Emma Frost and Polaris arrive to complicate the lives of the time-displaced mutant team for the foreseeable future. “It was always our goal to bring Emma back into ‘X-Men: Blue,'” the editor said, saying that while Frost has been through some dark times of late, she’s not turned into a villain."