I think (eventually) all income collected by the network should go to the delegates and the delegates should determine how the income is distributed.
--> Rewards Fund
--> Burn
--> Delegate Income
The shareholders vote for delegates that distribute network income in a way they agree with.
I would prefer if the delegates didn't actually get the money and then were expected to distribute it out to the appropriate funds (although that could be an acceptable compromise until a better system was built). I would like the network to do the distribution so that everyone can be guaranteed it will happen and they do not need to put additional trust in the delegates.
In particular, I would love to see a system where the delegates can make proposals that tweak the network rules which only become active if enough shareholders ratify it. Any active delegate would create a new proposal. If the majority of active delegates voted with approval, the proposal would be put up for consideration. Only one proposal can be up for consideration at a time. If the majority of delegates decide to do so, they can discard a proposal at any time. If more than a certain percentage of the stake votes in favor of the proposal up for consideration, then it is ratified and its rules become active in the next round. Perhaps in addition, if more than another percentage of the stake vetoes the proposal, it would immediately be discarded as well. Therefore transactions would only need a small addition to acknowledge the active proposal with a yea or nay.
These proposals could have parameters that define things like delegate pay rate (perhaps denominated in BitUSD), pay rates to different accounts (both mandatory and discretionary incomes) so they can use the funds for productive purposes (like development and marketing), interest rate caps on each BitAsset, prioritization of paying BitAsset interest, etc.