I've seen this idea kicked around quite a bit in game and on Reddit. Nightblades were meant to be the assassin class of the game (thus the assassination line), so why force them to be vampires just to have the fastest stealth movement speed possible? Leave the ability in the vampire line, but also make something similar in the Shadow line for nightblades. The abilities would not stack obviously.
Leave the ability in for the vampire line so other classes can have access to slightly faster movement speed, but don't force a nightblade that relies heavily on stealth movement, to become an undead flame target. The speed is very handy when tracking down targets, and setting up a rear attack. The class is very positional, and having to be a vampire to achieve maximum performance, just seems like too much of a crutch.
TL;DR - Keep the vampire line the same, but put a non-stacking stealth movement speed passive in the shadow line for nightblades.
Thoughts?
Surgical Incision
Former Emperor
USPS4