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There already kinda is something like this,… very subtle though.
The quest, where you unlock your mastery does spawn different enemy shades ![]()
But yeah, they could expand on this a little bit more, but it also means tremendous amounts of work.
This is will very likely be something post 1.0, if they ever going to do it at all.
This will be very likely not something for 1.0
There is a huuuuge thread about it with a lot of dev insight.
TL:DR: They really want to do it, but this cost a lot of time and ressources (mainly because of the voice acting, animations and 3D Art.