Just a suggestion, but since there arent any skins for the klg troops (Sentry/Operator/ER), we can the white variants in the pve missions as skins.
As for stat boosts, we need more unique ones in my opinion. Not just for the klg troops, but in general. Maybe we can set conditional boosts. Conditional boosts are stronger than normal but must be met to activate.
For example, sentry gets +5% crit chance only while invisible. A name for his skin could be Winter Coat.
Another idea is that it could change the element of the hero, for example, vanguard would turn into a bio once equiped. This would probably be limited to the klg troops though.