I’ve been playing guitar right handed for more than 55 years but I’ve never been able alternate pick fast lead lines. I finally figured out why and it’s genetic. I’m left handed! My right hand simply can’t consistently do the steady fast back and forth motion that’s necessary. There are many different wrist, arm, and finger motions that can work for different players (watch Troy Grady’s excellent YouTube channel ) but my right hand can’t do any of them reliably. I can not “vibrate” back and forth for more than a few strokes at high speed with my right hand. Here is the interesting part. I tried an experiment the other day and found I can easily ‘vibrate’ my left hand in the necessary motion for fast alternate picking. I wonder how long it would take to transfer my right handed skills and knowledge to left handed playing.
You did know you were left-handed before that though, didn’t you? 
There’s only one way to find out, I guess and that would be just to give it a tryout. I suspect that you’ll pick up the strumming or fast alternate picking real quick, which will be worth it.
The down side, is that I imagine fretting the chord shapes will be a nightmare. You’ve been doing that with your dominant hand for over half a century and will now be using your non-dominant hand for that.
I’d be surprised if it was not possible to increase the speed/accuracy of your non-dominant hand though with enough practice. Look at piano players for example.
Have a look at the Nitsuj lessons. I would expect you’d make a bit slower progress than him.
Good luck whatever you choose.
It’s an interesting question - I’m in exactly the same boat. I’m left handed but play right handed and I’m pretty limited when it comes to fast picking. I have a solution though … I don’t play fast.
I have wondered about changing over, but I’m been playing right-handed too long and I have a few nice guitars I don’t want to let go.
I guess it hinges on how important playing fast is to you. I’d be interested in hearing how it goes if you decide to give it a shot.
Yes, I’ve always know I was left handed but they gave me a right handed ukulele when I was about 6 or 7 and it felt fine. I don’t think I even knew people could play left handed until l I was 20 or more and I thought they were freaks. I figured it was like a piano, there are only right handed models.
Yeah, I can play fine right handed, and I do use alternate picking a lot. But I’m limited to going just a little faster than I can do all down strokes. And that’s fast enough for so many things.