Over the next year, the team will be 'spending more time focusing on various aspects of matchmaking such as intra-team balance, player conduct, new player experience, abusive behaviors, account buying, friend and teamplay aspects, high mmr matchmaking dynamics, and other issues in an effort to make the overall experience of playing Dota more fun for players of all levels.'
Solo MMR is now what remains, with Core and Support MMR coming into the game after completion of placements to allow for less unbalanced games if a Core player wants to try a Support role but has a high MMR, for example.
The removal of Party MMR was done to try encourage players to play with friends over worrying about their personal stats. The team stated that 'the game currently overly emphasizes playing solo and establishes a strong social reward mechanism for this, which causes many players to prefer playing alone than with friends.'
In addition to MMR adjustments, there is now a Role Queue feature available to all players. Dota Plus users have able to queue for specific roles for some time, but the update means the pools of players have seemingly merged as everyone now has the feature.
These changes have already been added to the game, but there is no notification in-game to bring attention to the changes. This has led to some cases of players not knowing about the changes, being assigned Support roles and the team being at a disadvantage when they refuse to play their assigned role or position. The r/DotA2 subreddit has seen numerous posts and screenshots of people refusing to pick a Support or not even realising that is their role, despite it being under their name.
The changes will be in place for the rest of the season and the team will seek direct community feedback after the conclusion of The International.
The full statement is available on the Dota2 blog page.