I like the thought process for the ult, but I don't feel it's too good for a 9 cost ult. If you compare it to Killjoy's Lockdown, you can see they're very similar in that they demand a massive ton of respect and are great to stall or guarantee space, but both have good counters—in Killjoy's case, it's molly/nade lineups and certain ultimates such as Sova and Killjoy, while in Viper's case, it's recon/angle clearning abilities and certain ultimates such as Killjoy, Harbor, and Gekko.
That being said, Viper doesn't really have much stopping power now that she has one molly. And if we're making her orb throwable then she's not gonna have it on the choke all the time, so you could even timing it.