I want a language that is small, clean, and can provide a lot of static guarantees. I know many people find static guarantees and unacceptable curtailment of their "programming freedom", but frankly I think it's the answer to many of the problems we face in software today. Small is another thing. E.g. Go and Scheme are small. C++ and Scala are large. You know what I mean..
Now, static typing is just one kind of static assertion[1] I'd like to have. Side effect isolation (i.e. language-enforced purity) would be another feature I'd like to see become common. For example, the D programming language has a "pure" keyword that lets you mark a function as side-effect free. (In Haskell, all function are pure by default, and you escape the confines of purity via monads.)
I'd like to do research into (inventing) other forms of static assertions. One thing that's been on my mind lately, has been static "complexity assertion" for programs. I don't know if this even possible, but it would be nice to be able to ascertain before running a program, certain time & space complexity bounds on it. This would perhaps require us to drop the programming language itself to some level "slightly below" Turing machines -- but this in itself could be achieved via a keyword like D's "pure" or something more elegant. (Note: my point is not that we're going to make the entire language non-Turing complete -- but rather that we'll have subsets of the language that are not, and this reduction of power would/could bring with it a greater possibility for statically asserting stuff.)
[1] FYI I made this term up. Let me know if there's something better that describes this.