How can tanking and healing be made more broadly useful in more "role-specific" ways?

[Shurrikhan]

So I have an idea for this that probably won't be that popular, but will solve at least one half of the problem: have dps stances for tanks increase their damage taken by 20% or so. That way, either the healer can keep more to healing the tank who is now taking far more damage, or the tank can keep up tank stance while the healer's dealing damage.

With DRK, it'd be tricky, but probably tie in a bigger increase to damage taken when Blood Weapon is up.

Alternatively, would simply reducing the passive mitigation and HP bonuses of being a tank, regardless of stance, have a similar effect, such that tanks are more reliant on active and stance-based mitigation?

This can be done by, say, giving each armor class merely a 25% bonus over the previous, such that tanks have merely 50% more defense than leather, down from 84%, reducing their left side Vitality to normal amounts, and making Fending accessories simply half Vitality and half Strength, rather than full Vitality and then additional Strength.

I'm not sure there'd be any effect on how tanks then fit into the picture in either case, though. That seems more like a nerf around which to simply rescript fights very slightly, still spending as little time in tank stance as possible, or else a much worse removal of viable breadth in tank toolkits.