My idea is that you need to level up to learn skills and need to research tactics and how to use weapons before using them.

How would you build in a leveling system while saying the game is made so every player (regardless of how bad he plays) has the same access to the game, the same amount of open-world-experiences? For myself I don't see how that's possible. If there are players reaching the level cap or the limits of boosting your characterspecs, how would the enemies adapt to them, regarding of the game being an open world multiplayer where everybody just runs around wielding bigger or smaller guns? I can't imagine character abilities growing larger, while the enemies stay on the same stage in certain areas (like moon), because they have to, if less experienced players are able to access those areas too. But I agree with you, that there has to be some kind of system. I just rather think it's going to be based on the guns not on the player himself. Maybe for the warlock in being able to find stronger magic abilities by reading ancient hieroglyphics in temples and so on. So level-based gadgets make no sense for me (unless bungie proves me wrong on this with another system :) ), instead every gun and piece of armor should be accessible to everyone playing the game and not just for the jobless lucky geeks. Of course anybody, who wants better gear, has to suit up to find them in the most dangerous and isolated areas possible to imagine :D. Also I'd enjoy some kind of marketplace area where you could buy/sell: weapons/items/clothing to ingame retailers. Not like a place where everybody can sell to anybody, but more like build in in the game itself, where prices get adapted by bungie relatively to the items desirability to the players.

You level up to upgrade your characters abilities, but new armor/weapons/etc is loot found on the battlefield.

I'd like this to be traditional RPG implemented into the shooter. Like Fallout, or Skyrim. No level cap, but increasingly difficult to level up. Everything should give you xp though. Missions, co-OP, social stuff...