With Hive that is not possible at the base layer. The inflation rate is already coded in for that and to change it leads to a credibility issue.

As for HBD, I can see the witnesses moving the savings rate up after the hard fork. That would only make sense.

I proposed the idea of Hive Savings Bonds at a 25% rate for a 1 year locked up of HBD.

Of course, what you propose can take place on Layer 2. Applications can build a APR on the staking of either of the tokens, paying out in their own token. That is very possible, in fact I expect it.