A lot is going to depend on what they do with the story in Shadowlands regarding the Lich King in general. Given how the two Death Knight starting areas have story to them, they would need to explain how future playable races will be able to become Death Knights.
Sure, some races can be put in the Bolvar starting area without much issue, but given it currently takes place before Shadowlands, it would be a bit odd to see some new races who had nothing to do in BfA appear there. Granted, I wouldnāt complain if it meant getting Saurok Death Knights.
Of course, they could change the Bolvar starting area to be more time-neutral. If Bolvar becomes the Lich King again, not much has to change. If another entity becomes the Lich King, then a model swap and new voice lines could be recorded. Add in some models of new playable races, and it shouldnāt be too difficult to do, as opposed to making yet another DK starting area for several new races.
Weāll have to see what happens in Shadowlandsā story. Still, Iām hoping weāll see future races be able to become Death Knights, and hopefully the Bolvar starting area isnāt necessarily time-locked. As I said, it could easily be edited to make it more time-neutral.