Disclaimer: I am not a theorycrafter, I am just trying to make sense of things. It is possible that I understand the calculations wrong, therefore take with a bit of salt. Or feel free to wholy ignore.
TL;DR: It looks like that math seems to imply that they can't do all that much about connection between active mitigation and the rotation.
Hm. Trying to wrap my head around all what was said and written, I am starting to think we might end up in a situation where we will want to crit enough times to get a full recharge pretty much guaranteed over the time it would take to get one recharge. There are several ways to get to it, albeit probably pretty insane all of them...
1) No haste. That means two crits over 12 seconds. With 2.6 weapon speed, that is 4,6 autoattacks. Ignoring the 0,6, that means that the average crit rate would have to be at 50%. That is, I believe pretty ridiculous and unlikely to happen.
2) All haste. Not going to bother with math here, getting from 12 second recharge to 4,5 one is simply in the realm of fantasy (talking 170%-ish haste).
3) Crit-haste combination. This is where it gets a bit funny. With just some 33% haste, we can get to 9 second recharge. Judging from the gear in this expansion, that isn't so far fetched. Considering that it would mean one recharge over the span of two SotR, we'd need one crit over the 9 seconds. The roughly 4,6 autoattacks over the time it would take to get one recharge, that means we'd have to crit once in four autoattacks. On average, therefore, 25% crit. This would effectively turn the 33% haste to a soft cap. I unfortunately lack the necessary understanding of probability math to get to relatively reliable amount of crit over four swings, although over the span of the fight, this theoretically should even out (considering starting with three charges, this should get it covered unless something really bad happens). Whether reaching 25% crit will be possible, however, is not something I know enough to easily figure out.
The above, however, has one BIG problem. It effectively means that with just passive stats and autoattacking, we can get near 100% uptime on 25% damage reduction - and that is with no mastery whatsoever. No rotation, no skill usage. Considering that SotR doesn't even trigger GCD, we would just have to follow a DPS rotation with keeping usage of situational abilities in mind.
I don't know how about you, but to me, that doesn't sound like active mitigation, automated mitigation sounds more accurate. Mind you, that is with no talents whatsoever, and in order for talents to change the above, they would have to take away some haste or crit in exchange for something else, which is by definition not going to be prefferable (as it would disrupt the 25%+ damage reduction).
So, I am quite wondering where Blizzard intends to go with this. It might be that reaching 25% crit rating while having 33% haste will be nigh impossible. It might also be that near-100% SotR uptime will not be a bonus, but downright necessary for top raid progression. However, the question then would be what else would there be for active mitigation. More importantly, why it wouldn't be in the preview, considering that it would pretty much be the most important thing for the spec.
So. I hope I have the math wrong? x)
EDIT: The rotation could, in theory, increase the damage reduction temporarily, but... That doesn't sound like "enough".