From what I've gathered, it seems the most likely long-term funding source for the SPS will be 10% of the total inflation. This would be "paid for" by reducing the amount of inflation that goes into the rewards pool from 75% to 65%.
With this change, the inflation would be:
- 65% Rewards Pool
- 15% SP Interest
- 10% Witness
- 10% SPS
Very dangerous ground in my opinion to drop them both at once and try to figure out which changes are having which impact.
Again, this gets into "my way" vs. "consensus" way. I'd prefer to see them split up too, but there are also some valid reasons to justify combining them.