In-game threat meter being planned?

During the Q&A portion of the most recent BlizzCon's Raid & Dungeon panel Scott Mercer, Lead Encounter Designer said:

"I know that UI mods are a huge part of raiding, and it's something that, you know, we're also talking about, in the future we're actually talking about putting a threat meter inside our game."

That's of course a statement simply saying that there are discussions happening, which is in no way a promise or indication that a threat meter will be implemented, but that it's something that's been in discussions for implementation.

Q u o t e:
ok... so you guys are talking about putting one in. How long does talking take?

We can only fit so many slumber parties into a month.

Q u o t e:
does it really matter? Blizzard's implementations of popular addons are usually pretty lacking compared to the original.

I think there's a misconception that we implement addons for the addon users, which isn't the case. The moderate to heavy addon user is probably never going to give up the immense amount of flexibility, customization, and control given by their addons. When we implement something, we implement it to provide something to those that aren't using mods, or don't regularly seek them out. They can log in and, hey! now I can see scrolling combat text, cool! And that works for the vast majority of people that couldn't be categorized as addon users, for the rest, no we don't pretend or fool ourselves into thinking we'll replace the mods you're already using.

Q u o t e:
So why not design them better, more customizable like the progenitors?

Because we want the default UI to be as simple and approachable as possible. If you want to customize your UI you have the ability by using addons.