This feature has existed in the consensus rules since basically the beginning of Steem. It was just largely forgotten about after witnesses set Steem Dollar interest to 0 years ago at a time when they were perpetually overvalued.
It has always been the domain of witnesses to decide this value. They could be updating it much more regularly if they wanted to.
Okay, makes sense in that Hivelandia is effectively a republic rather than a democracy. 😅
But since it doesn’t need a hard fork, what happens to HBD interest if some witnesses set it to 3% and some don’t?
The median value is used.