Good suggestion and you can see that I suggested that in the github issue that was linked from the post. However, it has downsides in that liquid rewards don't encourage people to have a stake in the platform, as intended with 50/50 or 100% SP.

Note that we already do have a version of this. People choose 50/50 when SBD is more valuable and often choose 100% when it is not. So the supply adjusts, just not very much and not quickly enough.