I think it would make sense for different types of transactions to cost a different amount. JSON-transactions are cheap because Hive blockchain nodes do nothing as a response to them apart from just recording them. Account creation, posting, voting, transferring coins etc. are much more expensive because the blockchain nodes have to do varying amounts of computation as a response to them.

The way to implement this could be to make RC's something that can be bought with HIVE or HBD and have the price reflect the dollar cost of the computations done as part of the transactions. When you power up HIVE, you get a certain amount of RCs. What if you'd only got any RCs when you power up at least 1000 HP?