By simple, you mean easy?
What about Java? Its easy, modern in the way you describe, has a good concurrency story, multiple great IDEs, can compile to a static binary with commercial JVMs, or experimentally in OpenJDK9. Really big ecosystem. Huge commercial backing. It just maybe fails at historical baggage and syntax.
Kotlin fixes those last two. And Java 10 will also fix a good chunk of the syntax complaints.
In all fairness though, I think you're focused on nitpicks that have no practical benefits. You're asking for a language with a better user experience. Which is great, as it can make programming more pleasant, and I'm all for it.
That said, I'd focus on language changes that provide functional value. Haskell adds a powerful correctness layer at a low expressiveness cost. Go adds a useful CSP concurrency mechanism with green threads, as well as being friendly to containerisation. Erlang and co add a great deal of reliability features and massive parallelism with first class actors. Clojure gives you powerful metaprogramming, state of the art immutability and a similar CSP layer as Go, while maintaining the access to Java's large ecosystem. Kotlin adds null type checking, and better functional primitives. Rust gives you safe memory access without the performance overhead of a GC. Chapel allows for super parallel computing. Scala gives you OOP with the safety layer of Haskell on it. Nim gives you faster python, with type safety. Crystal gives you faster Ruby with type safety. Etc.
Those are the languages that challenge the status quo, and have a chance at bringing real value in terms of the average output they result in when used to program with.
A slightly better UX for Java or Python is a hard sell. Its like the famous Unix quote: "the most dangerous enemy of a better solution is an existing codebase that is just good enough." - Eric S. Raymond
Java, C#, Python, Ruby, C++ are all good enough, even UX wise, to be displaced by something that doesn't offer compeling functional value. At least, in my opinion.