AFAIK, there haven't been any special asssesments (beyond annual dues).
I do not expect any in the future as dues include a component for replacing furnishings, roofs, etc. The only possible exception might be at VB or HHI since they are on the coast and more susceptible to hurricane damage.
That said, Disney has insurance and since there was no special assessment for VB owners after the damage from last year's storms, I would be surprised to see a special assessment anywhere. It could happen, but I don't expect that it will.
JMHO. YMMV.
Best wishes -