Resource credits have their own pool, and the RC "price" needed to perform operations on the adjusts dynamically. If the supply of HIVE/HP were to contract a lot, it is entirely possible that 1 HP could be enough RC for a lot of activity.

Likewise witnesses can adjust the fee for new accounts. It was 100 STEEM at one point. We could adjust it to 0.01 HIVE if that made sense.

I don't think converting HIVE to HBD is problematic in any way. Finally, as the price of HIVE goes up, less needs to be converted to create a given amount of HBD.