wat? pve legendaries require raiding? WAT? MADNESS! Embers will prolly be boE, but dont count on cinders to be boE - there is abs NO way they will be boE, nada, zero, nil.
Seeing how OP the staff will prolly be, id guess that even at the end of the patch you wont see anyone selling it because not everyone will have it.
And dont compare it to Shadowmourne(which was sold by many guilds) because the effect on shadowmourne was actually some small aoe, while this one is def going to be in the range of Atiesh/Valnyr.