Rader was a serial killer, and so far, Kohberger is a mass murderer. HOWEVER, Rader DID commit mass murder as well. If we're going to talk about crime, one way to do it is to compare one crime to another. That's pretty much how basic research into crimes takes place, whether academic or investigational. Profilers don't just make stuff up, they study past crimes.
SO, Rader's first kill (perhaps) was 4 people.
That makes Rader one of the more unusual serial killers of all time. Was BK planning to kill again? I bet he was. But he wanted to start out at the "level" of someone like Rader (or DeAngelo or Bundy). When people here on WS pondered way before the arrest if someone like BK could exist (basically like the movie "Copycat"), I was skeptical.
I'm not skeptical now. I think it will all come out when BK, himself, writes his own book, just as his mentor did - but he won't want a ghost/assistant writer. If he's prohibited from publishing as the lead author, he'll find someone to publish it for him or self-publish it.
OTOH, he may decompensate pretty badly in prison, down the road. But I think he'll pull himself together, get his hour a day in the prison library and write a book about himself, comparing himself to these other killers whom he studied and admired.