Valve have recently announced some controversial changes they will introduce to Dota 2's MMR systems. The first one is that party and solo MMR will no longer be separate, followed by role-based rating for core and support players.
Matchmaking rating (MMR) is something that keeps getting constant updates in just about every competitive game that exists today due to all competitors wanting to brush their skills against those of their peers in the most balanced way possible.
Valve are taking similar steps with Dota 2 but their latest changes are not likely to sit well with everyone. First up, they are removing party-based and solo-based MMR since the game was apparently too hostile to grouping up. Players will seemingly have unified MMR which is supposed to allow for more teaming up.
On the other hand, it is basically a free boosting service for anyone willing to go into a match with a group more skill than themselves. Valve didn't specify how they will counteract this potential issue just yet. They did, however, state that such issues should be minimal.
The second change is the introduction of role-based MMR which is supposed to make up for the lack of additional MMR numbers caused by the party and solo MMR fusion.
Another use for role-based MMR is apparently to ease players into spots they are not usually comfortable in. Therefore, if you are a core main thrown into a support role, losing the match will not impact your peak MMR. The same works for support mains.
This concept looks fantastic on paper but it has its own issues. For example, players will be thrown into lower MMRs regularly, impacting how much practice they can get against equally-skilled peers.
League of Legends attempted role-based MMR as well and it wasn't met with that much resistance initially but grew to be the most reviled thing in the game since the Stopwatch mastery, especially because high-ranked queues seemed to go on forever. It was scrapped later on.