Lictors should be given a 3+ save, toughness 6, Monstrous Creature status, calvary movement, No scatter when deepstriking, and 5 attacks.
Thats quite a bit of a boost for no points increase. Again, as this thread has pointed out, they shouldn't be main-battle units. They merely need enough of a boost to make their intended disruption role actually work.
3+ save is a lot for nids in general, not to mention a lot better than the original. Perhaps 4+, or allowing them to take EC. This isn't all that important though, as this doesn't keep them safe from hidden fists. I'd prefer a T increase instead.
But not to T6. Thats quite beefy, and there's no way you can justify him being as tough as a hive tyrant or carnifex. All he needs is T5 to avoid the hidden fists that devour him so readily.
Ditto for MC status. Lictors are not huge assault organisms, nor are they on par with the other two MCs in terms of mass. Also, a
stealthy monstrous creature is practically an oxymoron. Perhaps give him power weapons, like the broodlord (and only maybe at that).
No scatter I agree with, along with increased movement of some kind (maybe fleet, maybe cavalry, etc). A creature who's
only job is showing up in the midst of the enemy for an ambush can't be scattering away into uselessness, especially if its so slow that it can't move around in their ranks and cause trouble. These emphasizes his stealth, ambush, and disruptions roles.
5 attacks is a lot, perhaps 4.