d) Find an incentive mechanism that detects and penalizes people who do (2) regardless of whether they succeed or fail. I think the solution here is to make mining "quasi- deterministic". Deterministic mining means there is only one true history. Quasi-deterministic mining means that there is a limited set of alternative histories. I'm working on a pure proof-of-stake system that does a combination of (c) and (d). The system would use txns to measure "time". I will post a brainstorming thread about it shortly. I would appreciate comments. [Much too big of a change to be a fork of PPC.]
as usual good points. I agree - having an incentive for including transactions suddenly provides incentives for block history rewriting. The only way to compensate for that is to penalize events which indicate rewriting attempts. We don't have a solution for that yet. So I am looking forward to your brainstorming thread.