Is double gas steal a viable strategy in PvP?

No it is not.

He would have a huge economical advantage, as you send out your probe so early and You invest in 2 gas without using them. But a good opponent would immediate take his second gas once he sees the gas steal to prevent this.

This way you are stuck with a really bad economy, he still can tech to Stalkers, add 1-2 gates and push you with his first units. You will have lost more than 150 minerals with your strategy.

But even if you steal both gas he can add more gates and push you with pure Zealots. Depending on your micro you can kite those with Stalkers, but as everything is delayed you will have too few units to be efficient. He will have 4 Zealots while you have 1 Stalker. 2 Zealots attack your probes and 2 chase the Stalker. Even if you can defend your economy will be screwed.

During this time your opponent will have either expanded or killed your 2 gas in his base.

This is if you opponent can cope with the situation and knows how to react. Up to gold or platinum league you might throw off your opponent because he does not know how to react and win.

It's not used because Protoss's gas timing is so standard regardless of build and you'll have to cut probes and scout extremely early to get there in time, in most cases. I imagine the standard counter is just to drop another Gateway instantly and chrono out Zealots that will do huge economic damage. The only way I see this working is if you manage to do it on a 2 player map with proper timing on your Probe scout while walling off your ramp back at home and probably 4-gating or 3-gate expoing while using your superior Stalker numbers for map control.