Ian Lance Taylor is working on split stacks. This will permit the stacks of gccgo goroutines, which are mapped to native threads, to start small and grow as needed. This will of course be usable from C as well, and should be welcome news for the millions-of-threads!!!1! faction.
Tom Tromey is working on making GCC an incremental compiler: GCC will run as a server and maintain a model of the user's program. When a translation unit is recompiled, GCC will re-compile the minimum necessary. One of the goals is to make GCC a backend for IDEs that do stuff like autocompletion based on the program model (Interview, paper from GCC Summit).
People from Intel and others are working on transactional memory. Sections of code can be marked as atomic, and their temporary changes will be saved in thread-local storage. The semantics will make it appear as if transactions were protected by a single global lock.
It's a great time to be writing a Lisp->C compiler! :)