I am mostly interested in anything that requires C/C++ implementation and AlgoDS.
For that reason I would love to work in any of the following (in that order of preference):
Sorting algorithms benchmark and implementation
Enhancing amcheck for all AMs
TOAST'ing in slices
Thrift datatype support
Having recently worked with Thrift, I recommend ... don't use Thrift. The library is awkward to work with, it isn't very source-compatible across versions.