An update on Battle.net outlines how Blizzard feels about the current state of matchmaking in Heroes of the Storm. They describe the positive impact of some of their recent changes as steps in the right direction, and emphasize their commitment to make further strides going forward. One future plan is to restrict the number of specialty heroes that can randomly be placed on the same team. Here's word:

Our rules for Supports and Warriors in Quick Match have helped level the playing field in terms of team composition, but we’ve also seen feedback from the community indicating that receiving several heroes who have limited lane presence, or fill unique roles, on one Quick Match team can make for a challenging experience.

We’d like to limit cases like these, and we’re currently planning to implement a new rule for Quick Match that will prevent more than one of the heroes listed below from being placed on the same team:

• Abathur
• Cho’gall
• Lt. Morales
• Murky
• Nova
• The Lost Vikings

As with all of the team composition restrictions we’ve implemented so far, parties can still bend this rule. This means that you may still see heroes like Abathur and Cho’gall on the same team if those players entered the queue as a party.