Your motherboard can split the x16 from the CPU into two x8 slots (two slots! not x8/x8 in one). That's the full extent of its bifurcation abilities (bifurcation requires extra hardware, it's not just a firmware thing). So you can add two m2-pcie cards using two passive adapters in two slots...
In olden times the HD light was driven by a disk controller. Some M2-PCIe adapter cards have pins for connecting the case LED. Otherwise it's entirely up to the motherboard to generate it (or not).
Depending on how strict with terms you want to be...340x0 cards could be used for 3D acceleration. Since they were full fledged CPUs, they could do 3D even if lacking dedicated 3D functions.
It's a shame that the optical audio port has never been updated. It's stuck in the year 1982 forever. But still beautiful because of the electrical isolation.