No one was under the illusion that Simon Cowell would be easy to replace.

And, as speculation about who will sit in the hot seat he’s vacated on American Idol continues, two more big names have hit the radar: Both Justin Timberlake and Elton John are on producer Simon Fuller‘s short list, according to The Hollywood Reporter.

What about the future of the current judges? Sources tell THR that FOX is looking to lure back ex-Idol producer Nigel Lythgoe, who has said he would clean house if it were up to him.

The judge most likely to be left standing is Randy Jackson, according to THR, but it would also be difficult to let go Ellen DeGeneres, who has a multi-year contract with FOX. According to a source in her camp, she’s prepared to fulfill the contract, THR reports. Kara DioGuardi‘s deal is year-to-year, and it has yet to be renewed.

Elton and Justin join Chris Isaak, Shania Twain and Harry Connick Jr. on the list of possible replacements.