I can’t answer every question known to man based off the vague prompt I answered. I took a pretty good stab at it. :) I also don’t know what makes things learning worthwhile to every type of person.
> Do Elixir's ideas improve your thinking when working on other languages?
Most languages do, and I’ve already mentioned Elixir’s unique features. Although, in a way, it will make working with other languages feel painful if you do any concurrency. Elixir and Erlang change the way you think about and work with concurrent processes and do it in about the best way possible, as it’s built in to the language in a core way. Learning how to deal with immutable data, writing pattern matching code, and functional programming are also all pluses.
> Are Elixir developers in demand compared to other languages?
I don’t know how to judge this, because define demand. The answer is ultimately relatively irrelevant to me and how I look for positions. If you’re asking, in a roundabout way, whether there are well-paying jobs in Elixir, the answer is yes.
> Is it a fad language?
I don’t know what a fad language is. Stack Overflow is not the global truth, and the plot is linked without context. Elixir has had its official forum for seven years now. It was created around the beginning of 2016, which roughly corresponds to the peak in the data you posted with a bit of lag in the downturn, as might be expected as people learn of the new forum.
Lastly, making a decision based upon what is popular now is not a long term thinking decision. What is popular now was making head winds 10-20 years ago.