I have read the Wardancer career path and the Wardancer entries from the Wood elf army list. Here are some thoughts that you may want to consider or just ignore completely. They are only ment as a reflexion.
- The Forest Demon career is listed as a Elite career. It should have four talents slots instead of three. Additionally, Elite careers have between 12 an 13 advances instead of the normal 10. Finally, the "Any" talent slot only appears in careers with the "Heroic" trait. Nevertheless, I don't think it will be game breaking, just out of the "norm".
- After reading the Army book, I would design the tattoos more in line with the Gutplate of the Maneater rather than in line with the Troll Slayer. For example:
Talismanic Tattos: Soak 1, Defence 2, and you may spend fatigue, stress or wounds once per to session to ignore a critical wound.
- As for the Bladesinger, it appears to be some thematic contradiction between the warhammer 3 rpg and the army book. While in the army book they say that wardancers tend to fight with many different weapons, dual swords, two handed, spears… the rpg seems to favour the dual wielding style wardancer. In the army book they say that since they fight with so many different weapons, units of wardancers may add 1 to their Strength and 1 to their attack characteristic. You can for example give a career ability that would be +1 damage to all melee attacks (the same as the giant slayer), although it is a bit boring. You can use the assassin career idea (very nice one) or a variant of it like for example
boon +1 damage
boon boon: +1 damage, perform a free manoeuvre
An option to keep your proposed career ability would be to restric it to a certain type of action cards, for example
boon boon: add the secondary weapon DR to the total melee damage of any melee action card with the Ritual Dance trait.
Although I still think +5 damage is way to much.
I hope this may be interesting for you, but at the end is a matter of styles.