this is a very interesting idea. I especially like Idea 2 where the amount of HBD that gets interests is linked to the amount of staked Hive. For following reasons:
While not increasing the effective number of HBD interests paid, it would be possible to increase the interest rate to a higher level (20 - 25%). The HBD interest could function as USP (unique selling point) for Hive which would give a new use case to hive stake and make hive more interesting.
Case analysis:
If Hive goes up in price, people tend to swap HBD for Hive, the number of HBD in savings would go down, the interest level could be increased with the same amount of HBD distributed as interests.
If the price of hive goes down, Hive is directly linked to the interest payments of HBD. People would swap hive for HBD, thereby increasing the quantity of HBD in savings but at the same time, the quantity of Hive stake would go down. This means that less HBD would get interests. In this situation, people would tend to purchase Hive and stake it to get full HBD interests.
I don't really know what would happen if HBD would lose it's peg to the $. In this situation people might swap or sell HBD. With fewer HBD in savings, it would be possible to increase the interest rate and give a new attractivity to HBD and indirectly to Hive.
After thinking this through for only a couple of minutes, I believe that this mechanism would give a new use case for hive power. I don't see in which situation this could have a bad influence on Hive and HBD but I might have forgotten some things :-)
RE: An Open Idea: Linking HBD Interest Rates to Staked Hive Power