There was a throw away line that the Time Lords had brought the master back, and the fact he came back in the TV movie shows it is not a hard capped limit, there are ways around.
With The Doctor being the last Time Lord now, I imagine there are some ways around it - either throw away or meanigful. Steven Moffat may well not be the show runner by then, so while I imagien he would take pains to have it all make sense (look at how he ensure any retcons made sense this series) a new show runner might just decided to ignore any reference to it.