I have no idea why this hasn’t occurred to me before. And I can’t find it anywhere (though it may be out there, who knows…)
So we now have Fortitude and Undying and all those Elven traits with “immune to A, B and C” (okay and Fireproof too, but that was a natural progression). Why not apply this, also, to Slayer traits?
I mean, I’m not saying figuring out which ones fit is easy, but it isn’t much of a stretch to do something like “Bane Slayer - 2x skull damage to Daemons and Undead”. Figuring out the various pseudo-Wildfolk, hm, a bit harder or much wordier. “2x skull damage to Beasts and Monsters” could be… Critter Slayer.
Make some otherwise passed-over troops a bit more cool, maybe create some new strategies for some of the stronger ones, etc.
(Whether this would result in 4x damage on specific dual-types is, well, up to the devs - I say yes though! Given Tau with two Slayer traits seems to do 4x damage to those dual-types, consistency should rule here.)