The regional leagues are beginning to plan for Rift Rivals 2019. The for-fun tournament usually takes place during the middle of the summer split to forge a rivalry and get some international practice in, but three regions have announced that they will not be participating this year.
The Oceanic Pro League (OPL), League of Legends Japan League (LJL), and League of Legends Sea Tour (LST) will not be participating in their usual Rift Rivals bout this year. (Note that Garena Premier League, or GPL, has been rebranded into the LST within the last year.)
The announcement on the OCE LoL Esports website notes that the rivalry between the three regions never really formed and the viewership for the tourney was similar to that of a normal OPL match. That being said, the region would rather take the high production cost that would normally go towards Rift Rivals and use it to help grow the smaller scene around the OPL, like the Challenger Series as well as high school and university leagues.
Fear not Rift Rival fans. There will still be a tournament between NA and EU, as well as one between LPL, LCK, and LMS. Information on those tournaments should be announced soon.