Marvel wants to clean up a lot of their titles, continuity, plus combine the MCU and 616 origins.
This is basically their Crisis on Infinite Earth's aka "Battle World" They haven't been too specific, but it sounds like they might even get rid of the Ultimate universe by having them duke it out on Battle World and have the winners remain as the 616 versions, such as female Thor vs Ultimate Thor or Age of Apocalypse versus House of M versions.
As far as MCU, they're changing Magneto's children's origins to not have them be Magneto's kids to match the MCU. I'm thinking they want the MCU to be their Ultimates now since it's become such a huge thing in mainstream media and the Ultimate universe kind of ran it's course by now.