This is a good point though I'm not sure if denying others interest could be a profitable strategy. By doing so you would most probably deter other investors from buying the currency whatsoever which would negatively impact the price of your own stake.

I just had the idea that one could completely change the incentives in my dual-token blockchain model. Instead of paying interests to minter accounts, one could simply give them the right to make transactions with lower transaction fees than free accounts. Alternatively, one could set a minimum transaction amount for free accounts and no limit for minter accounts (which would then be suitable for microtransactions). In the latter case, minting would be done by small users rather than by big investors. Though this would make minter accounts cheaper and more susceptible for attack scenarios.

It appears that one could use a GHOST-like protocol to protect a PoS/PoW blockchain from colluding minters and bribing attacks. Such attacks normally result in orphaned blocks, so a special reward for including them into the blocks of the main chain would make collusion more difficult/expensive. The more orphans are referenced, the higher would be the new block's score and thus the likelihood that it will become part of the main chain. In addition to GHOST, transactions of the orphaned blocks referenced in the main chain would be considered as issued at the time when the referring block is created. Nodes censoring certain transactions (and blocks that contain them) would have a hard time.

As a minimal alternative, one could just reference orphaned blocks in the chain to achieve consensus over the orphan rate (as a moving average calculated over the last k blocks). That would allow to set the minining reward (interest rate) according to the orphan rate. With higher the rate, the higher would be the mining reward and thus the incentive not to take part in the censorship/collusion.