I really like the idea, as it would really mean (potentially) that x/D could get real benefits from statting Wisdom, for example. Though perhaps, to compensate what, e.g., an R/D, would lose in statting more Wisdom and less pattk, you would have to include a smaller m/pattk bonus as well. Better healing is good, but who would want a DPS character with worse DPS and better healing?
Values would be tricky, as if you weren't careful D/Rs would swap to R/Ds etc., but certainly doable.
The only other issue I can think of is the resellability of gear (or how easy you can buy your pattk/dex/wis gear) when every Rogue, Warrior, etc with a different secondary class would need different statting. Though, it could be cogently argued that that would be a good thing, reducing demand, increasing diversity, encouraging people to make their own gear.