When there is enough outrage by the public to force their hands. Considering the second best player on last years Eastern Conference Champs got suspended for PED's, and it barely registered on the radar, I think there is a long way to go before people start paying attention.
Stern is a master of spin, and sweeping things under the rug. As long as he is in charge, I think Lebron (not to mention Perk and Rondo) will be fine.