The available supply is just an analytical concept that I used to highlight the fact that not all of the supply is available to the market. Once the hive balance on the DAO is flipped over to HBD it will have no meaning. It's a good way of measuring the deviations from the "scheduled" emission given a long enough timeframe.
As long as we have a hive balance in the DAO the ebb and flow of the available supply is (in my opinion) a good way of measuring the market trends in the mid to long term given the fact that we have hbd to hive conversions and (hopefully soon) conversions from hbd to hive.
In the short term the flow to (and from) exchanges is a better predictor of how the market percieves hive. That is maybe something worth discussing in another convo.
If forced to try to calculate a scheduled rate for an essentially unpredictable thing, I suppose the best that could be done would be to do a moderate worst case analysis and assume the daily budget would max out every day and assume a fixed price of Hive (to eliminate the essentially unpredictable price of Hive from the equation).
Totally agree.