Rewind most of the ideas you mentioned (as I personally believe they aren't really feasible).

Simply give any nukers a massive Enmity- trait when spells have been bursted. The reason no one magic bursts anymore is because they pull so much hate.

As for skillchains - give a small defence-down type status effect on the mob where melee / magic does a little more damage for a short duration (say 15 secs). Similar to that of a weapon aftermath effect - however decreases resistance on the mob. Potency of defence down varies depending on the lvl of the skillchain tier and weakness.

For example doing a darkness skillchain on a mob like Rani (who is darkness based) has a minimal defence down effect, however doing a light skillchain give Rani +5-10% Damage taken. (or something).