In another post, I explained why a vertical progression hard cap is so important to many players, and why the perception that it was part of the philosophy of GW2 led to such an uproar when an item stat progression system was intiiated by Arenanet.
Playing GW2, I realized one of the problems with any vertical progression whatsoever is that, after you do it once or twice, after that it largely becomes a chore when all you're really doing is trying to max out different characters to play with different professions, races, builds, etc. If there is ongoing vertical progression, it becomes grind trying to keep all your characters maxed out.
So, why not a purely horizontal MMORPG, or an HMMORPG?
Picture this: you log into the character creation module, and part of that is a weighted stat distribution system. You get to not only pick your race, looks, etc., but your stats, traits, skills, etc. You also get to pick your gear, which has strength and other stat requirements (to create a trade-off system for gear & stats). IOW, you get to custom design a fully maxed-out character.
When you leave the character creation module, you can either log into the world, or log into a training area to test out your build and practice with it. You can to into WvW, PvE, or PvE areas. By playing in those areas, you can gather up various kinds of rewards with which you can buy different traits, skills, weapons, gear, and other horizontal commodities. Let's say that when you log into any action area, your character is committed to 10 traits and 10 skills with weapon-swapping ability. Let's say that when you first log into character creation, you have 30 traits and 30 skills available, and an assortment of standard weapons and gear (that all have a max distribution of stats). You can pick from the starting variety to initially build your character from.
However, by playing PvE, WvW or PvP, you gain rewards that can be used to purchase more traits, skills, different kinds of weapons, different kinds of gear; you can unlock many cosmetic variances, animations, more dye control, a wider range of pets both useful and cosmetic; keys or passes that can take you to different areas of the game, mounts, player and guild housing - all sorts of horizontal content. A lot of this can also just be bought from the cash shop.
The trait and skill system would be based on the use of "non-comparables", much like the League of Legends system, but instead of each character being locked into a certain set of non-comparables, the player can custom-build his or her characters however they find suitable, mixing and matching stat distribution, skills, traits, weapons and gear. They can collect a stable of characters (or character templates) to use as they see fit in the game.
The beauty of this system is that developers would no longer have to figure out how to keep the non-end-game areas relevant, because in fact the whole game (outside of the optional training area) would be the end game. No more starter or mid-level areas to get your character "leveled up". You can just start in a single city (whatever your race) and head out any direction you want, go anywhere you want, because the entire game is designed for max-level characters - which you start the game with.
Another key aspect of this is that the developer could initially create a relatively small world because most of what now occupies MMOG worlds would be unnecessary; areas for leveling your character up. Like League of Legends, they could even start with relatively few initial traits, skills, weapons, gear, etc. It could be modest start-up to test the market, and then easily grow by adding to the existing game.
Think of League of Legends in a full 3D world like GW2 or Rift but with PvE and WvW and fully customizable characters and zero vertical progression whatsoever.
It might only be a niche game - or, it could be as popular as LoL. It's time a developer looked into making an HMMORPG.