For some reason, Byron never gets enabled after meeting the requirements to begin this quest. Even if I manually enable him myself, despite him running up to me (and following me around), he refuses to actually speak to me to begin the quest.
Heey, I actually just posted on your wall. I actually had the very same problem. Please revert to an earlier save, before you used the console. then wait for 5.0.26 to drop, should be any moment now. Be sure to read the changelog!
This has been fixed. It is because you did the Lord's Mail quest before starting Shattered Legacy. Upgrade to 5.0.26 and per Ice's instructions, type setstage dbm_shatteredlegacy 0 in the console. Then wait for a day or two outside Whiterun stables.