The last phase of the staff has horns on it similar to that dragon in the pictures so I'm with you guys and betting that's Tarecgosa.
I think it's great. What's the point of a legendary with no story and no history that just drops off a hard boss?
Sulfuras was awesome - you had a to craft its first incarnation then transform it into it's final form. Thunderfury was similar. Shadowmourne was even better. Dragonwrath may be the best method of legendary crafting yet - slowly evolving the weapon into its most powerful form with the support of an entire guild.
The question of who tarecgosa is could be a variable. In this case, we can determine whether she is in the staff or not:
#the variable would go here
if tarecgosa_is_evil:
print "She is trapped in the staff"
else:
print "She sacrifices herself to create the staff"
Uhm....>.> She's my mother
Nah I'm kidding...
She's MILEY CYRUS!
No sorry....
Well anyway, I seriously have no idea who's that dragon. But she has to be imba!
Lightwell! It's gewd!
Maybe new legendary is just a Blue Dragon-on-a-stick? Like, the last Resting place of it.
Life is short Glory is eternal