No one knows for sure. Blizzard is being tight lipped about that. This is on Blizzard's website:
What is the function of the Gem in the Diablo II Battle.net Chat room?
While we cannot reveal the purpose or function of the Gem in the Diablo II Battle.net Chat room, we can say that it is working correctly and has more than exceeded our expectations. Also, Blizzard employees cannot confirm or deny any rumors regarding this Gem.
“When a team doesn't double me, it's like they're disrespecting my game.”
"We're going to get another one next year, again -- back to back to back."