My answer might sound a little philosophical.

If making money is your top priority, then you can go for iOS development, DevOps or backend engineering.

If it is not, I would highly suggest adding more knowledge, learn about data sciences, artificial intelligence, or whatever you find interesting. Since you already have good experience, you can freelance to get your money in the meantime. You'll become a more holistic programmer/developer. Try working in a startup for a little less money, you'll learn exponentially more than you would in a large corporation. Frameworks, platforms, are tools to get things done. You could even venture to a product management role.

My honest opinion would be to zoom out and then decide. And there is nothing wrong with wanting to make more money either.

If it's high pay you're after then you'll just have to be good at whatever it is you do. The senior devs for any field get paid way better than the beginners/freshers.

Having said that, on average some fields are paid higher than others. Data science is definitely hot here in India right now, and not as many people are in it. As you noticed, iOS is also a highly sought after skill these days, again probably because not as many people are in it. Also, if you want to be where the future is going I have to urge you to check out React Native development and JavaScript development in general.

Cheers :)

I don't foresee Microsoft giving up on the smart phone wars. Windows mobile may be down, but I don't think it's out. They just need to try something different.

That said - why not consider Windows mobile development? If your going to start new and try a new language; may as well try one where there is minimal competition.

For a while, I was actually a huge fan of Windows mobile. The problem is and always was, a lack of good apps for it. Had good apps been available, I'd have switched (from using an iPhone from day 1 release)

In which country are you planning to work? In-demand skills depend mostly on the country you're in.