First off, my main issue is the 4 options only, it will hurt important npc, face it the NPC you remember in a game is the ones with plenty of dialogue.
No they don't need to be important in the game, neither Moria or Alvor was important.
Yes you can get by it doing deep nested dialogues, however it will be clunky.
The new dialogue system will probably also be problematic on pc.
If your character says something else than you see it will feel stupid, problem here is more how its presented, as they wanted to show the dialogues in an an cross rather than an list you only get room for 3-4 words.
That your character speak outside of dialogues, well normal people rarely speak load unless they talk to somebody. Small talk with companions, Insults to enemies curses then trigger an trap is ok.
Worst case scenario we get an babbling idiot as many Skyrim NPC, fear is increased that character commenting is shown as an feature not some tiny thing.
In short dialogue is the only reason why I have not pre-ordered just to be done with it. Everything else looks good.