Thanks for the advice. I just thought there would always be other candidates in front of me with Rails professional experience, so I would always be at the end of the queue. The dev bootcamp would be my strategy for moving further in the queue, but I guess that's not the only way.
Dev Bootcamp is not the only reason I want to move to the US and that's why I posted this question. My main goal is to have an interesting job in the US, but I was in doubt between applying for an iOS developer job from London or go for the dev bootcamp first and then look for a job where I could eventually use my knowledge on iOS and Rails, as I think it would be a good combination. I'm starting to be convinced that I should go for the first option and I'll continue learning Rails on my free time.
Thanks for your comments. I agree that I can learn Rails myself, but I assume the dev bootcamp would be a good proof that I actually know it and I assume I could learn more in less time. Besides, if I learn it myself, I could come up with an idea and build a web app, but would that be enough for a company to consider me (specially when there are probably many developers already with professional experience trying to move to the Bay Area)?
About the H1 visa, the problem is that, according to what I read on the internet, it's estimated that it will be exhausted by July this year. In the meanwhile, I was also told that J1 visa is a possible alternative, but I haven't investigated that possibility yet.
If a company decides to hire me, but is afraid I might be cheating on a technical video conference, I wouldn't have any problems to go to the US for a face-to-face interview, even if I would have to pay the costs myself, simply because I don't cheat. If they are happy with me on a video conference, I'm sure they would be happy after a face-to-face interview.