I think we could consider moving to it if and when the funding/budget system is proven, including shown itself able to fund a variety of useful value-add for Steem. Once that is demonstrated then it makes a lot of sense to look at social rewards in such a context.

Applying it to witness rewards is more problematic because of the circularity/bootstrapping problem. Without reliable witnesses you don't have a secure blockchain on which to conduct the voting or operate the budget system. Some blockchain projects have and are proposing to allow the substructure to be mutated by stakeholder vote, and this could be okay, but it is far more complex and riskier.