I don't know if something like this has already been suggested, so apologies ahead of time if it has been.

Spelldux
Classes available to: any class that's expected to 1x/2x+ in Spell Research (semis/pures)
Tier: Uncommon or Legendary
Requirements: For semis, at least 100 ranks of spells trained; for pures, at least 200 ranks of spells trained.

Spelldux acts similarly to Kroderine Soul, in that training in it gives the character redux (magical or physical), dependent on how much Spell Research the character has. For semis with at least 100 ranks of spells trained, each rank of Spelldux trained gives 0.1% 'dux per spell research rank over 100. For pures with at least 200 ranks of spells trained, each rank of Spelldux gives 0.5% 'dux per spell research rank over 200.

(Percentages and ranks numbers are guesstimates, totally open to tweaking.)

~Cylnthia Kythnis Ardenai
~Inquisitor of Kuon
~Rose Guardian, House Sylvanfair