Sorry for the delay in responding to this; I wanted to make sure I had all my info 100% correct before I said anything, rather than risk giving you incorrect or incomplete info.
So first off: the threat bonus from using taunts is not being removed. That's a tooltip change that was made entirely for consistency; every taunt increases threat generation while it's active, but it was only mentioned in the tooltip for a few of them for some reason. So that's just basic housekeeping.
However, separate from the tooltip change, we are going to experiment a little with reducing how big the threat bonus is on the 8.1 PTR. Currently, it's pretty massive, which is a holdover from when it was first added in Mists of Pandaria. Remember, back then active tanks were dealing huge amounts of damage (and thus, threat) due to the Vengeance mechanic, and so the offtank needed a huge threat boost to be able to keep aggro through tank swaps. That mechanic hasn't existed for a few expansions now.
Nowadays, in BFA, threat is once again something tanks need to keep in mind, and that massive bonus opens us up to all sorts of wacky issues as DPS (both from tanks and from damage dealers) increases. As one example, there's a risk that we end up in a situation where certain tanks need to use their taunt on cooldown as part of their single target rotation. That would be bad for several fairly obvious reasons.
So, we're going to try it with a lower bonus on the PTR and see what happens. Our expectation is that there is no tangible effect on your gameplay; you still use taunts exactly how you do now, and they have the same result.
I'm a little confused- you expect threat issues bad enough with DPS scaling over time that you worry tanks might feel like they need to weave Taunt into their rotations because it gives them extra threat, so you're reducing the bonus, taking away an option to deal with that apparent inevitability? Are you adding something else? What gameplay do you see arising instead?