Recently, I’ve been looking into language design, and I’ve had some of my own opinions about how things could/should be set up, but I was wondering:
If you could add any feature, syntactical or otherwise, of any kind, to any programming language, what would that feature be, and why do you think its needed?
Don’t.
A programming language so sophisticated that it programs itself. Sponge mods for all.
There are programs that let you program programming languages to describe and execute a program.
Just so you know, that really wasn’t intended to be taken seriously.
I wasn’t being particularly serious either. 
(Even though there are things like parser-generators)
Why not, this is interesting. But there is a lot to do to reinvent a new language.
A general purpose language that is made primarily with the intent of readability and efficiency while being both statically or dynamically typed as a compiler option, has a prudent amount of semantic control (somewhere inbetween C and Java), have functional programming, OOP, and procedural paradigms, reflection, runtime modification/code injection, universally deployable application archives, and should compile to a universal CPU architecture (that has only one instruction).
A language whose primary purpose is necrobumping.