t might be strange for the guy in charge of D&D R&D to say this, but here it goes: After the core rules for the game are done, we really want to stop adding so much stuff to the mechanics of the game and shift our emphasis to story.
D&D is a shared language. The rules serve to make it easier to talk about the game and make stuff happen. They take abstract concepts and give them clear meaning. When we say "5th-level wizard," we know what you can do and how you do it. We know that because we play D&D. Someone who never played the game would be utterly lost.
A language works best when everyone who uses it can communicate efficiently. If I described my character as a "prime tier ensign," that doesn't mean anything to you. Could you guess what my character wears, what sort of weapon he might wield, and what special abilities he uses? Any answer you give is a pure guess.
For that reason, in building classes, character options, and everything else in the game, we need to stick to things that make sense and resonate with you. That's why we've adopted things like specialties and backgrounds as tools to organize game rules. Rapid Shot and Precise Shot are abstract things that aren't really clear. You can only understand them by knowing what they are. They don't stand on their own in a meaningful way. Describing your fighter as an archer, though, makes sense to anyone. Your character uses a bow. That's self-evident from the word archer. There are still details to study, but the general idea evokes a key fantasy archetype.
The trick is that the list of things that resonate is shorter than an unbound list. It's a challenge, but it's one worth tackling. Realistically, I'm willing to bet that most people didn't start playing D&D because they wanted to take Rapid Shot. You probably wanted to play an archer, or a sneaky thief, and so on. The most resonant elements arise from outside the game, in the myths and stories that we're all exposed to.
The other side to this coin is that with a much-reduced emphasis on turning out new rules mechanics, the material we make receives more playtesting, development, and care. If you want to make an archer option, it has to be a good option. You don't get a second chance at it.
So, that's the general philosophy on expanding the rules of the game.
Mike Mearls is the senior manager for the D&D research and design team. He has worked on the Ravenloft board game along with a number of supplement for the D&D RPG.