devtrackers.gg
So, casters have started saying whether or not they'll be casting. Here is the thread saying if they will.
LEC:
LCS:
LCK:
LPL:
Confirmed to have no representatives.
List in Progress - Will be updated when more information comes out
Disclaimer from Medic himself:
External link →Just going to jump in and say we were told we can announce individually. I don't think a full announcement is coming out, but just because you don't see someone tweet immediately, doesn't mean they are not doing Worlds.