Monte and Chobra released information about this in last night's Masters broadcast and I have yet to see a thread made about this, so I thought I'd go ahead.

Next week of Masters will not feature any organizations playing each other in traditional Masters matches, but will instead have two days of All-Star matches. On Thursday, March 27th is the "Legend Match" and on Sunday, March 30th is the "All-Stars Match". I'm not 100% certain on the info in this thread, so if anyone has corrections or can verify, it'd be greatly appreciated.

The Legend Match will feature an All-Stars matchup where fans vote for players in each role. Only top laners can play top lane, only mid laners can play mid lane, etc. Two all-star teams are formed by taking the two most popular players from each role, and these two teams will play each other (presumably in a normal 5v5).

Monte and Chobra also confirmed last night that several players are coming out of retirement to play an El Clasico of LoL - the old Season 2 Azubu Frost roster and the original NaJin e-mFire roster, which are the following:

The All-Stars Match, on the other hand, features two teams composed of the 10 most popular players in Korea, regardless of position. I don't know if the roles they then play will be decided randomly or whether the teams get to choose amongst themselves, but I do know it'll be hilarious. I also don't know if there are any showmatches along with the All-Stars match, but I hope there are.

You can vote here, although you need to have an account to vote. Please let me know if there are any corrections to the info in this thread.

EDIT: Thread not intended to be a "riot sucks and OGN is better" thread, just one that spreads awareness about these matches next week