As someone who's played and loved a Warlord, I want that name to remain. Warlord was one of the most important and significant advances of 4e, and I think it's important to acknowledge that they've earned their right to "Core" status if you're going to get 4e players into 5e. I could accept losing Warlord if we're doing a return to the base 4 classes and nothing else, but if Paladins, Rangers, Sorcerors, or Bards show up, the Warlord had better be there to keep them company. The Knight and Marshall have been class names that have never really taken off - the Warlords have earned the right to join the core under their own name, not having to steal a name from a lesser class.