In an interview on WWE's The Bump, Rey Mysterio revealed that he would put his mask on the line if the opportunity was to come forward. 

WCW SuperBrawl IX was when Mysterio and Konnan lost to Kevin Nash and Scott Hall in a hair vs. mask match. For the first time ever Mysterio had to remove the mask. Due to how significant luchador's masks are to their identity, Mysterio had to get permission from the official Lucha Libre Commission to wear his mask again.

"If the opportunity came about, I would jump in a heartbeat [on putting his mask on the line again]. I think that's what makes Lucha Libre exciting and in this case to bring Lucha Libre to the WWE, and show the WWE Universe the excitement behind the mask vs. hair match, or the mask vs. title match. You know you put your heart out there in those matches. I would actually love to jump in the ring one of these days before I retire and put my mask on the line against something that is well worth it."

Thanks to WrestlingInc for the transcription.