I've never tried it myself, but presuming you build the kernel in modular rather than monolithic mode, wouldn't the incremental compiles during git-bisect et al

I've never tried it myself, but presuming you build the kernel in modular rather than monolithic mode, wouldn't the incremental compiles during git-bisect et al already be pretty quick? You'd only be rebuilding the modules whose source files changed, and those (presumably) wouldn't be pulling in the entire header tree. (Or would they, with that being "the problem"?)