Speaking personally, not on behalf of the core team:
I agree this is something worth addressing. if let x = x { } is so incredibly common that it clearly deserves some form of privileged syntax. Personally I do like if x? { /* x is non-optional */ }, though I'm not good at spotting potential parse problems from adding sugar like this.
I agree that the clarity-over-brevity argument doesn't address tooling. But I also think there's a strong case just for the sake of clarity, irrespective of tooling. if let fooAutomationViewController = fooAutomationViewController { ... } is not clear. Swift removes verbose ceremony that can obscure clarity, and this clearly fits with that direction.
Regarding the commonly rejected list: people should take note of it, and the core team has added to it recently. But it needn't be treated as inviolable – we have also removed entries from it when sufficiently well-motivated proposals have come along (though note, the proposal that prompted that removal was rejected following review).