If it is the right time right now I am not sure about, but inevitably, Swift will be a massive, widespread programming language community. Actually, it already is, but right now 90% of the people using it are iOS developers. However, if you are interested in Swift for Linux and backend development, check out Vapor, Kitura, Perfect, or any of the other web frameworks. In light of the recent 3.0 release, I think it is a great time to get involved and learn Swift.

No. Source: I only have seen titles with iOS in them most of the time.

Yes. It's a neat language. Runs on linux too.

Yes, it's the most interesting new language since Go. It does a lot of things right, and much more importantly it's much better supported and moving much faster. For instance, there's no good go IDE/debugger setup right now (just the other day my boss was complaining that he's %10 as effective as he would be with a debugger, he's exaggerating, but not that much.) Also the way Swift has evolved so quickly makes me believe it's going to be a significant language. I don't think Apple intends for Swift to suffer the same fate as Objective-C (Which was never proprietary and which was superior to things like Java, and came out before Java, but was never widely adopted outside of Apple's ecosystem.)

Right now Swift has Playgrounds, no other language has that, excellent support in Xcode, works across platforms, and the language makes a lot of really good design choices and is improving rapidly.

What more could make a language worth learning?

As for whether it's the best language for you to learn next, that depends on what you have learned in the past. If you've never done a functional language, the next language you should learn is Elixir. Erlang is the only language I know that gets concurrency right, and Elixir is a ruby syntax and nice extensions on top of Erlang. Elixir is the best way to write erlang and erlang is a correct functional language with genuine concurrency (Haskell might also get concurrency right, I don't know, but Go does not and no other language or actor model framework does it right. It has to be in the language.)

If you've only done scripting like Python or Ruby and you want a compiled, heavier or more hard core language to learn, I think Swift is the ideal candidate for the next language to learn.

Ask yourself if learning a proprietary language from a company past its prime is the best thing to learn with the time you will spend.

There is plenty of talk about progressive web apps, and how engagement is massively boosted by not forcing an app install on a potential user before they have mental buy in into what you have on offer.

And swift on a server? Just no. Remember Cold Fusion?

Learn Python. Learn Haskell. Learn F#. Hell.. learn Java (disclaimer: I'm not aware of what your current skills are)... But Swift.. worth a quick look and a peering into its syntactic sugar, to be used only when absolutely needed - I.e. you get 100k to develop an Apple Watch app.