The quest chain that starts with defeating the Shade of Eranikus ends abruptly with Umbranse. Although Chal Fairwind is PvP flagged Alliance, if you are Horde and you have the quest  In Eranikus' Own Words Umbranse will speak to you, and Chal will not attack you unless you attack her first.
Blizzard representatives have hinted that the quest chain will be extended in the future. As of Patch 3.3, the chain still has not been extended.
This section concerns content exclusive to Cataclysm.
Umbranse has moved from the camp near Everlook and has now apparently taken over Mazthoril, revealed in a quest line that involves the Crystal of Zin-Malor. He is no longer friendly.