Map Badges: The Opt-In Ranked Alternative We Didn't Know We Needed.
Let's face it. Riot is not going to give us a ranked queue for Dominion or solo TT. ARAM is too chaotic for a traditional ranked system, and SR is unappealing to many players, or they prefer team builder over draft to get a more cohesive group.
Despite this, many players want a way to display their skill, which we currently don't have. Let's say you want to form a ranked TT team, but you don't have enough friends who play it. How can you recruit other solo players to ensure that everyone is at your same skill level on the map? SR rank certainly doesn't apply, and TT W/L alone never tells the whole story. This is exactly where a display of skill would help.
We have the measurement needed to measure that skill in the form of hidden MMR/elo (ARAM is currently an exception due to smurfs and dodging. See this post for more details on combatting dodge scumming, or this thread for a pick type outside of a full unlock to counter smurf advantage). Simply displaying this rating, however, is not an option. A large number of players have what Riot refers to as "ladder anxiety," and prefer to not know how they compare to others. Revealing MMR outright would be upsetting and potentially discouraging to these players. Comparative systems need to be an opt-in experience. There is, however, a way to apply this MMR to create such a system, without needing separate queues and ranks to split and thin the community.
Introducing map badges.
Map badges are an opt-in system to display a player's complete skillset, rather than restricting it to just a ranked border. It lets players choose which areas to show off or keep hidden, while being non-invasive for players who would prefer not to know.
Let's start with the system as it appears for players who want in. Borders have 4 corners. Each corner, along with a slot on your profile page, could host a badge of a different map, displaying your relative tier within it. The badges would have a design representative of the map, such as a crystal for Dominion or a nettle for Treeline. These tiers would simply be based on percentile MMR/elo among all players (even those who do not opt in).
Top 70%: Silver Top 30%: Gold Top 10%: Platinum Top 2%: Diamond Top 0.1%: Master Top 0.01%: Challenger
It might also be encouraging to list the MMR gap between a player's current score and the threshold of the next tier up, without giving exact values for each, along with an estimated number of wins which, if consecutive, would move them up.
Great, we've turned normal elo into a semi-ranked calculation. How do re restrict it to an opt-in experience?
Enabling display for each map would be an option on your profile page, defaulting to off for all. Upon enabling one, you would put your own badge on display on your profile and border, as well as enabling yourself to view other players' badges of that map on the loading screen for that map. This part is key. If you do not opt into the system, your allies' badges for the map you are currently on must remain hidden. Your MMR is going to be similar to theirs due to how matchmaking works, and it is too easy to infer that a person playing among silvers is also a silver. Displaying badges for other maps is ok, since the skillsets required tend to differ wildly, and that's where enabling your badge for view lets you show off. Finally, for the players who don't even want to consider skill in other areas, there should be an option to disable badges and borders entirely from view. Why this option doesn't already exist for borders I do not know. Normals players intimidated by the plat in their teambuilder is a problem that already exists.
Play a match of SR and show off your Dominion diamond. Let your ARAM partners know that you're TT plat. Have procpestive TT ranked allies able to look at your TT-enabled profile page and see if you sync up. Be proud of your accomplishments on any map in the game.
One last important part, players who opt in deserve access to end-of-season rewards based on their highest map OR rank. We work just as hard as ranked SR players to play and improve our skill on our favorite maps, and we demand the same rewards.
As a bonus, there could be a unique end of season reward for each map you achieve a minimum tier on, in addition to the normal skin/border. SR could have ward skins, TT could have custom sweeper particles, CS could have particle effects on channeling, and HA could have custom snowballs (like the butcher's bridge orange) or poro accessories (like the Braumstache).