Elixir hits this pretty well.
Simple syntax ... Check
Erlang-style concurrency ... Double Check (has _exactly_ Erlang style concurrency)
Powerful macro system ... Check, steals Lisp's amazing macro system verbatim
high-level declarative constructs ... Check, Pattern matching, `case do` `with ...`
Note the "other two" platforms it would run on would be the secret of it's success, so web and mobile.
JS eventually got all of the things he asked for.