The problem with questions like these is that they aren't the right question really. It never has been about Stamina being king or Agility being king or anything of the sort. The question is: how can I optimally gear myself for the sake of my raid, the boss fights, and most importantly, my healers?
The answer to that for Druids is actually quite a range of acceptable gearing strategies, and is largely dependent upon fights and what your priority is. Generally speaking people like myself and Reesi and many others gear heavily into Agility because there is a rather sharp diminishing return on Stamina past certain thresholds. You rarely hear people call it that, but that's essentially what it is. All Healing, notably your healing in particular, comes in discrete chunks. This is lessened somewhat by HoTs from Druids and such but nonetheless, it comes in discrete chunks. Damage likewise definitely comes in discrete chunks, meaning that Stamina and EH have break off points where you don't really gain much because the next discrete chunk of damage kills you regardless.
I'm not sure how long ago you played but a really easy example that people seem to remember better than more recent ones is Brutallus. You could only obtain so much EH to survive X hits post his Stomp, and anything beyond that point pretty much was wasted since if the extra hit landed without you getting healed, you died. A lot of damage in DS particularly comes in nice fat chunks like this, although some is broken down differently like Focused Assault. Aside from Heroic Madness Impales (25man particularly with its 1.2mil spike), Druids in roughly appropriate gear for the content they are Tanking pretty much acquire a suitable amount of EH for Healers to heal for all other fights without much consideration for Stamina. Generally speaking, if you're giving your Healers enough time to get you healed with the EH (Stamina, Armor, etc) you have, then you have enough and more isn't really going to help all that much unless they struggle to hit that window.
An easy ways to tell if you have too much EH is if on X encounter, you never seem to ever dip below a non-negligible amount of Health (ie 15k+ or so). If you never dip lower, than that extra padding of Health isn't doing you really any good. Reserves are nice and all but if you never tap them, it is technically wasted itemization. This includes having enough EH to take a whole additional hit and so forth. Yes it is nice to know that should your Healers all simultaneously get distracted with a cat in the toaster you can eat 15 hits from Morchok, realistically you just don't need that kind of cushion. Obviously if you DO sometimes dip then by all means, keep the extra EH.
Agility stacking has the advantage of boosting our mitigation (via Dodge and Mastery improvements) as well as greatly increasing our DPS. DS isn't exactly a low bar for DPS to pass, particularly if you aren't rocking any of the uber cool trinkets, set bonuses, or a few Dragonwraths, and dealing several thousand extra DPS just in pure Bear form Tanking isn't to be scoffed at. Add to that the ability to go Cat in many fights while simultaneously Tanking at times and you can really add a lot to the raid (and thus why Feral is being split in MoP, but I digress).
TLDR Version: If your Healers are comfortable with your damage intake and you aren't ever spiking and your raid is not in any real need of some extra DPS boosts (and you don't really care about spicing up some of the fights with some pro kitty action), Stamina stacking is OK. If however you want to play around with Agility, there is no danger in doing so provided you don't waltz up to Heroic Warmaster or Heroic Madness in all LFR Agi-gear and say "Imma deck you in the shnoz!!" and hope to do well.