Valve are attempting to address numerous complaints and issues involving the Dota 2 community and matchmaking system, with some experimental changes. These adjustments have been explained in some detail in their latest update.
Starting off by giving some reasons for the changes, they said over the next year they will be focusing on all sorts including "intra-team balance, player conduct, new player experience, abusive behaviors, account buying, friend and teamplay aspects, high mmr matchmaking dynamics" and more. Why? They want to make Dota 2 more fun for people playing at any level.
The first set of major experimental are already up and will last until the end of the season. When the experiment is over, they will be requesting feedback sometime after The International tournament concludes.
So what's changed? Firstly, they've removed separate Solo and Party MMRs, something they know is "controversial" and they're not "fully confident" in it actually being a good change. One major reason being that (with the normal system) it favours people playing solo. They also believe their matchmaking system is balanced enough, that playing with a friend with a higher rating shouldn't affect the overall balance but more work is to be done on that.
They also moved the Ranked Roles feature from the Battle Pass into the main game, along with having both Core and Support MMR numbers (with leaderboards for both). So now, when picking a game you can select different roles and you will be matched based on either your Core or Support MMR.
The full post with all the details can be viewed here.