Basically, the concern now is that Widows can be out before the 5 minute mark, whereas Protoss cannot have an obs before 6:42 at the earliest--leaving a potential window for 2 WM weapon cycles before the Protoss can have detection.
I am not a particularly skillful player, but I don't understand why the Protoss cannot simply either wall in, or FF the ramp. A tight wall-in (one that leaves no holes at all) will completely prevent the Widows from entering your base without any need for defenses (although it will require you to tear down a pylon later). A nearly tight wall in (leaving a tiny corner blocked by a zealot) can also buy you enough time, although it does mean donating the zealot and microing a stalker and a probe to keep the corridor closed (probably donating the probe as well). Lastly, FF on the ramp requires you to be good at FF placing and timing, and requires you to go sentry first, and possibly delays your obs a little. However you are now allowed to go sentry first vs. terran because a sentry can now safely push a reaper out of your base, and this will leave you with sentries, an obs, and a robo--allowing you to go zealot/sentry/immo which is a perfectly good unit composition against T. It also doesn't require you to donate a pylon.