After many years of players requesting the feature, Blizzard's Overwatch is getting crossplay support between PC, Xbox, PlayStation, and Switch, massively expanding the available players across all platforms. That should go a long way to improving the matchmaking experience by giving players access to others who are closer to their skill level, as well as speed up the process since there will always be people ready and waiting to play.
How will this work when it comes to a difference in controllers? Blizzard will not have cross-play in Competitive mode, so if you're trying to rank up, you won't have to play people using a superior control scheme (read: mouse and keyboard). Cross play will also be disabled for console players by default, though they can turn it on if they wish to enjoy a wider range of opponents. PC gamers will also only ever be matched with teams of PC players, or PC and console players. There won't ever be a situation where PC players will be matched exclusively against those languishing with controllers.
PC players will have the option enabled by default, but console players will need to make a Battle.net account on their console of choice in order to enable it. There they'll also be able to make groups of PC and or console gamers to play with.
Cross progression won't be available at the launch of cross-play, but it's something that the Overwatch team is working on enabling in the future.