Kotlin is far simpler than Scala which has a big emphasis on functional programming and OO, so not going to be super popular soon. It's also behind Kotlin in good ide support. Clojure is simpler, but mainly focuses on functional programming and is a lisp as well, so will also not be a great candidate for the masses.
Functional programming has surged strongly in popularity these last couple of years.
As pointed out, other JVM languages also have "Java interoperability" as top priority. Clojure does.
Clojure is getting popular lately, why isn't a "great candidate for the masses"? Because it is a Lisp? During most of the 1980s, the #1 programming language to teach children how to program was LOGO, which is basically Lisp in disguise...
If something doesn't have algol syntax, it generally doesn't do well with the masses. Look at where Common Lisp & Clojure sit on the TIOBE list(do they even break the top 20?) FP is picking up some steam, but I fear lisp never will especially with such fragmentation of language and vendor. I'm not really familiar with Logo, but it doesn't sound like it had parenthesis or brackets like Rebol (something to make it homoiconic), and since it is not in use anymore...that might be proving my point.
C, C#, C++, Java, & JS could be said to have a derivative of Algol syntax. That covers probably 90% of all software being actively written in the world.
