We've written about Totemus before here on WoW Insider-- even though it does a lot more than just time your totems as a Shaman, that's mainly what I used it for. Not only did it provide me with a visual representation of what my current totem situation was like, it also gave me a heads up whenever my totems were failing, reminding me to put them down again. But of course since that's mostly what I used it for, I may not have a need for it after patch 2.4-- along with the other UI changes, Blizzard is going to be putting a totem timer into the default UI.
It's not the first time they've "stolen" addon functionality, and it definitely won't be the last. And while a few reports are coming in from the PTR, it remains to be seen whether this change will actually replace more complicated addons (my guess is no, considering how simple Blizzard's timer looks).
But expect more of this in the patches to come-- everyone heard that Blizzard wants to implement a threatmeter into the default UI, and a "DamageMeters" type of tool would likely be appropriate for the default UI as well. Blizzard has always had the luxury of a great and hardworking addon community, and I wouldn't be surprised to see them start taking advantage of that luxury more often.