There are more creative ways to add tanks with different playstyles than adding an evasion tank.

Give them an active mitigation rotation.
Tanks can be as varied as dps. The argument that adding more tanks is pointless cause it won't get more people to play is dumb.
Not everyone who plays a dps likes the same things (e.g. cast times or dots or melee or even types of animations). It's the same for tanks.

Admittedly the scale may be smaller for how many people like the role.
But it's just wrong to assume that if they introduce a new tank, they wouldn't be opening to window for some people who don't like the war or pld.

Plus only adding dps classes cause that's what more people play will just take away from some of the current tanks and healers. So the alternative is not much better.
Ideally they'd add at least one tank class and one dps class next time. Then it'd be more balanced.