Thing is, people need to stop thinking about progress solely in terms of raiding. A properly-geared caster is already in partly T5-T6 just by virtue of getting the BoE/BoP epics from tailoring. An enterprising tank can be in gear very much on par with T5 with many of the new badge rewards. My alt warrior (leftover Kara loot, tons of badge gear) has successfully tanked Lynx in ZA.

My guild who hadn't set foot in SSC/TK cleared ZA a few weeks after it was released (we have since gone into SSC & TK). It's demanding on your coordination when you're at that outer-edge of the gear requirements for it and a whole lot of fun if you're in that kind of guild. Also, the rewards for my main (shadow priest) are BETTER in general than all of SSC/TK. Moreso in 2.4 with the spell haste change.

So I'll be making time to hit ZA as often as I can between 25 man raids because frankly the bang for my buck is higher, and the challenge and cozy feeling of a hard 10-man is tough to beat. But progression is still very much a 25-man game.

The timed events were a great idea for giving overgeared players something to care about from the instance. We've gotten 2 chests a few times but 3 is hard at our gear level, and gives us something to strive for.