I ban AZ 'cos, well, or some infantry covering it. Wyches no longer get haywire grenades, and Scourges' Haywire Blasters are rather short-range, and Scourges themselves are T3 (like any other human, tau or eldar), with 4+ armor and 6++ invul saves (like Sicarians). Techpriest Dominus can be trouble though, as he is one of the best Imperial HQs who has 5/6 chance of self-healing, 2+ save and a ton of nasty wargear (one of which makes all his CC attacks Haywire).
EDIT: Damnation, I forgot. Titans are immune to Haywire now, same way as Gargantuan Creatures are immune to poison/sniper weapons. Dominus still can be a trouble due to yet another of his relics.