A new browser will not have to implement kv-storage itself, either it can let the user polyfill it or quite easily copy another browsers implementation.
Polyfills aren't a panacea, and we shouldn't blindly excuse anti-competitive behavior or attempts to monopolize the direction of an otherwise open platform that we all share and depend on.
Now the problem is "Oh no we're converging to a single implementation, we need to diversify it!"
I don't know which is better but it is kind of funny to note.
1. Early IE and netscape era: OMG there are so many browsers
2. IE6 dominance: Oh no we're converging to a single implementation... [and they don't follow the spec]
3. Rise of Firefox and Chrome: "OMG there are so many browsers
4. Chrome dominance: Oh no we're converging to a single implementation... [and they dominate the spec]
We do not have that problem with Chrome.
The core problem remains the same.
Should the only browser be from one company? No.
Was IE6s problem that it was from one company? No.