I still think taxed hashes are an ok solution. I know it has disadvantages, but I think those are small enough to consider it.
I also kinda like the idea of taxed hashes when implemented right (e.g. using actual time spans instead of block heights to specify a time frame where solutions have to be revealed) ;-) But I also fully trust HunterMinerCrafter when he says that this is not the correct way to go ... he has proven to me that he has a much better eye for the "big picture" than I have.
I am eager to dive deeper into a discussion why the current (and any other) approaches discussed so far are bad, and how we could possibly come to a satisfying solution

Sorry that I have been offline today, I will be online the entire day tomorrow.