But Challenge modes are returning in 6.0, which Ian Hazzikostas confirmed:
There are a slew of achievements for completing challenge modes, as well as getting all the medals. I remember when they first came out, I thought it was great - it was something that allowed skilled players to compare themselves to others, and it wasn't gear which made you the good player - it really was skill as everyone was 463 ilvl.
The Grumpy Elf's post "I support removing Challenge Modes" had the shock factor title that is so typical of TGE, but upon reading it he touched upon things which I hadn't considered.
Challenge modes were designed with the concept of the game we have now. The game we have now is changing incredibly next expansion. Not just a minor change in abilities or what they do but huge sweeping changes and all those changes will effect challenge mode balancing.
Hit and Expertise will be gone. Fewer gem slots. Less enchants. Stats squishing. What does that mean for challenge mode gear? It might mean there will be certain CM BIS you have to get just so you can get it done... and who knows what bugs may play up scaling new items down to 463. Removing them altogether and making a new WoD is just fine, and there will be new ones for Warlords of Draenor for those who want to keep doing them, with new rewards, so I now agree with TGE about their removal. Imagine the programming nightmare!
Personally, I love challenge modes. I love pushing myself, seeing what I can and can't do, and at the moment trying to be as cheapass as I can get when running them (cheap food, cheap buff etc). I feel like because I've done them I am a half decent healer, maybe not a fantastic one but at least decent. I still doubt my abilities because I am unable to get Proven Healer as a druid, when everyone says it's so easy. Yes I have my golds, but I will always feel like I've been carried there. In Proving grounds, I still get stuck halfway through wave 28, and I've put it down as I may be good but I'm not THAT good. Lucky it's not some kind of test to get into raiding or anything.
There's still a fair bit of time to do your challenge modes if you want the gear or the mount. Thunderspank had a good run for challenge modes with pugs from OpenRaid, and I know Riptyde often pulls people from OQ. There are people who want to do them, like you, looking for the right group, and maybe just maybe, you might find that one person in a 100 who might make it onto your friends list. But make sure you're confident in your healing, if you're a healer! Or you could end up with a rather shameful dent in your ego.