The majority of the work to enable LTO will be to implement object mode linking in Bazel. Object mode also enables faster compilation over static mode linking, so supporting object mode likely will have more benefit in itself than supporting LTO.

Object mode = skips generating the archive files and instead statically links the raw object files statically into the final binary
LTO = Code generation in the link time step, which allows for optimizations that require the compiler to know information across compilation barriers (ex. inlining functions with implementations in external targets)