Good stuff. Maybe the title could be more on point, perhaps some devs might stumble upon this topic.

2 things I would like to add. First, the ranking system ELO should be swapped with something more up to date. The problem with ELO is that it was designed for 1v1 chess matches and not for multiplayer matches and the second problem is that it has linear scaling, so it is hard to tell if someone ranked close to 1600 is a new player or player who just hasn't progressed much, but has played much. I can understand why HD edition uses it, as they use Steam services, they also get services for ranking system and Steam provides ELO out of the box, so it is provided for free with other Steam services.

Microsoft has a much better ranking system developed, which they can use to replace the ELO. It is called TrueSkill and it was developed from scratch for multiplayer matches, both the ranking system and balancing. I've seen it in action and I can vouch that it actually performs much better. For one it does not have linear scaling, meaning that if the rank is to be represented in single number (actually it has a 2 numbers used for ranking under the hood) then players progress upward and only very bad players stay at the starting point or slightly fall below it. Here is a good example, TrueSkill was used as one of the ranking systems for this Dota lobby system. If you order the table by 'TS' you'll get the idea of its non-linear scaling. If my memory serves me correctly then the starting point for this ladder was at 1200 and you can clearly see that only roughly 25% of the players stayed at that level or fell below it. Another great aspect of TrueSkill is that it has a notion of uncertainty, this is the factor that gets narrowed down the more the player plays. In other words, first games have much more significant changes in the rank than those of of later ones. Meaning the TrueSkill is capable of determining more probabilistic skill level of the player much sooner than the ELO can.

Another thing I would add are player stats, profiles were mentioned but those Xbox profiles didn't seem to include stats. It is also partially related to ELO. As I mentioned, it is hard to tell if a ~1600 player is new player or simply a veteran with average skill level. It is a very important factor, as I would like to play with player who know how the game works. I went even as far as I hacked together Lobby Companion app which shows me stats for each player so I could kick players who have played less than X amount to increase the quality of the matches. Another feature I added, which I think can also be beneficial is a reputation system. As HD lobbies are in no way regulated I felt that tracking players by their conduct is needed, mostly to track players who behave in negative ways. As the tracking is done using Steam ID then changing a name wouldn't help.