As Angelica said, 7th Gen will have no new Eeveelutions as confirmed through Eevee's Pokedex registration in a Japanese trailer, along with the reveal of Eevee's exclusive Z-Move which showed all eight existing Eeveelutions.
Excluding 1st Gen, we mostly get new Eeveelutions in even-numbered generations anyway so 8th Gen definitely can't be ruled out at this stage.