Just make tank stances a bigger deal
Problem: Tanking is a bit boring right now.
Reasons: SE wants a low skill floor, so that new/casual/lazy players can get through MSQ, and so DF PUGs aren't a total nightmare. So they're never going to make managing enmity too difficult.
But tank players want a high skill ceiling, otherwise they're bored. So, once aggro is taken care of, we need a way to contribute.
Solution: Make stances more meaningful. Like, more than double their effect.
DPS Stance: You can't survive a tank buster, or a bunch of adds. You just can't do it. You also generate no extra enmity. In return, your DPS can be 80-90% that of a DPS class. Essentially, when you pop DPS stance, you become a slightly sub-par, squishy DPS.
Tank Stance: You can't do much damage. Not much at all. But you generate loads more enmity, and your health is similar to where it is now in tank stance. Basically, you're an old-fashioned tank.