#1 Roster Cuts

Just as the NXT pipeline, and perhaps the NXT roster, on the whole, may dwindle if there aren’t two main roster brands to ultimately move up to, the existing main roster may face some trimming if there’s just one big roster.
Top stars like Roman Reigns and Becky Lynch will presumably be just fine and remain on top regardless of the brand situation. Stars like Asuka and Baron Corbin may see their stock drop slightly to more middle of the pack roles.
Underused talents like Shinsuke Nakamura and Rusev could see their stock sink even lower. The talents in truest danger of all, however, are ones like No Way Jose and Curt Hawkins who struggle to garner TV time under the current circumstances and may disappear altogether with twice the stars for WWE to feature on each show.
WWE will surely keep some less known stars around to have reserves in the event of others getting injured, or because they have long term potential or can fill specific roles.
However, things will be getting less sure-footed for those talents management feels already got their show, or who are already on the cusp of the chopping block when roster cuts come.