Well, just as the title says. I personally think that every game should be modable, come with an editor, and have community created content. It happens often enough that something the players create vastly improves or adds to the original game. Skyrim is the best example with it's roughly 40.000 mods in NexusMods alone, but there are also a ton of other mods for a ton of other games. Like the guys who made a complete remake of Half-Life 1 with Half-Life 2 graphics, and gave it away for free. Or the GTA 4 mod that gave you the abillity to play as Iron Man, shooting rockets, flying around, etc. Just 2 examples out of a vast sea of possible creativity. Thousands of players can just come up with more ideas than a development team of a few hundred people at most.
So, what do you guys think? Should stuff like the Creation Kit that comes for free with Skyrim be the norm these days? Just imagine the possibilites... Imagine Dark Souls being as modable as Skyrim. Hundreds of bonus hours of gameplay, entire new continents... I think i just drooled a bit.