The question was to be divided into different topics, so here comes.
Julia is an expressive language, that is, it is a good tool able to do things, and it is also efficient in computing power usage.
All in all, Julia is about efficiency.
The ease and productivity of Julia, from the easy, fast base language to composable packages translate to the efficiency of development.
The computational efficiency of Julia translates to efficiency of computer uses.
However, let’s bite the bullet and look at this efficiency for what it really means.
A business with 2% of its cost in software wouldn’t risk ruining the business over 2%, and something more important like reliability (which Julia currently lacks) will be more important.
A project that needs lots of performance but can hire experts can use C++/etc because they can be fully optimized. While Julia can be easier to optimize in some cases, there are also a lot more C++ programmers. C++ is also more reputable as a standard in this front.
If the business just wants quick apps, python/etc can do the job. Many languages are also more familiar even if it’s not “python-like”, so those may be selected instead.
So, this leaves us at the intersection of efficiency in development and efficiency in compute power. For example, some indie games, tech startups, some low power embedded devices once static compilation becomes practical, etc.
However, this very intersection is also full of competition, for example, python’s numba, a bunch of small languages, python with native code library, etc.
What is Julia’s role. Where will we see the killer application that pushes Julia forward?