Still if FB hits T-tar is dead... bu tI guess he would be the only one who could have a shot at setting up SR without being obliterated... Ferrothron and Deoyxs would both be OHKO'ed pretty easily
I'm not sure you quite get how this is gonna work.
1. First and foremost, B-Kyurem and W-Kyurem will be tested out in standard play (where Stealth Rock is omnipresent,) so the Uber metagame won't really matter at all if W-Kyurem isn't found broken in standard play because of Stealth Rock.
As an aside, 125/90/90 defenses is pretty mediocre in Ubers, especially if you lose half your HP on the switch due to Stealth Rocks. Compare to some actual Uber walls like Lugia: 106/130/154, Ho-Oh: 106/90/154, Deoxys-D: 50/160/160 and Giratina: 150/120/120.
Those are good defenses for Uber. Now compare to some other Uber Pokemon that aren't primarily walls. Groudon: 100/140/90, Kyogre: 100/90/140, Dialga: 100/120/100, Giratina-O: 150/100/100,
Manaphy: 100/100/100 and an insanely better typing, Reshiram: 100/100/120, Zekrom: 100/120/100, and Arceus: 120/120/120
2. Regardless of it, none of the Stealth Rock users in either OU or Ubers will ever seriously face a W-Kyurem directly. They'll show up (probably on one of W-Kyurem's teammates whom they can wall/scare off,) set up and then proceed to either a) die or b) go back in reserve just in case they're needed later. In light of that, how easily W-Kyurem can kill them doesn't matter. They'll get to set up 90% of the time, screwing over W-Kyurem in the process, and then their job is done. They can die in peace. If nothing else, they'll probably set up on your switch to W-Kyurem. Assuming you kill them, they can summon their W-Kyurem check and force it out, meaning it'll be affected by SR when you switch it back in. There's a reason Charizard is stuck in RU even though it can easily KO Ferrothorn.
Anyway, for the topic. I'm kinda on the (apparently) less popular camp that wants it to remain Dragon/Ice. Failing that, I'd like a pure Dragon type Uber legendary for once.