I can think of:
-Carbon spider on the back (with Sram XD slots)
-Titanium M5 bolts (stock are steel)
- The lockring inside the last 4 smaller cogs is super heavy!, so I could think of removing that, bolt the 4 cogs straight to the rest of the cassette body, and add a sleeve just like Ethirteen is designing their high range cassettes, but that would require a clamping system to the freehub somewhere.....
393g total for the 13sp 9-42 version is a lot, considering Ethirteen made a 298g 9-46 11sp a while ago. (TRS race first gen).
