The Death Knight creation bug, which does not allow some players to create Death Knights on realms which they don't have a level 55+ character on, will be fixed by rolling restarts.
The restarts will take place tomorrow (Wednesday January 21st) at 5:00 a.m. PST / 8:00 a.m. EST. Each realm should be down for a short period of time, and the restarts should only take around 15 minutes. Oceanic servers will see their restarts take place at 12:00 p.m. PST / 3:00 p.m. EST.
We can safely assume that these restarts will correct the issue. However if they don't, look here for more information.
Additional Note: There is no new information on the Wintergrasp bug