IMO 154 special def still makes Ho-oh pretty easy to get in, esp on unstabbed t-bolts. Bulky ones aren't going to be taking much even from something like Gengar. It's 90 speed is what makes it lose, but sacred fire still makes it uber IMO.
Some samples calcs with Ho-oh, I chose gengar for it's powerful SAtk and Suicune because it seemed like the best OU counter with enough Def to handle the 130 base Atk
Max HP/Max SDef (+nature) Ho-oh vs. Max SAtk Gengar.
394 Atk vs 447 Def & 416 HP (T-bolt 95 base power): 122 - 144 (29.33% - 34.62%)
4hko w/ leftovers. (assuming no stealth rock or sandstorm)
Stealth rock makes it a 2hko =(
Max Atk Ho-oh (with Choice band) vs. Max HP/Def (+Nature) Suicune
591 Atk vs 361 Def & 404 HP (Sacred Ash 100 base power): 88 - 104 (21.78% - 25.74%)
Seems good, except for the burn.
Max SAtk (+ nature, no damage boost) Ho-oh vs. Max HP/Min SDef Suicune
350 Atk vs 239 Def & 404 HP (T-bolt 95 base power): 200 - 236 (49.5% - 58.42%)
(60.16% chance of 2HKO with Leftovers, near 100% chance with SS)
Dmg Calc used:
http://ownpurpose.com/damage_calculator_test.php
My own prediction: If this thing becomes OU, it would easily surpass other pokes to become the #1 lead (with choice scarf). Burning pokes and doing massive dmg on the switch is pretty awesome and eases on a lot of prediction. Heatran is an easy 1HKO with EQ and can't really do anything back short of HP Rock.
On the stall side of life, it can even outstall slower HP Rockers with Roost. Things that can hit hard with Stone Edge can't really counter it because none of them (maybe Magcargo does) like to be hit with a Sacred Ash burn.
As of now many teams can live without using stealth rock, this thing can really overcentralize certain teams to the point where every team carrying a Ho-oh might need at least 1 or even 2 rapid spinner and a weavile, spiritomb or other pursuiter for ghosts.