Ropetown

1) Pre-purchasing loot is a good idea, and it's something I've always kinda wanted to do, but it basically requires coding to work well. I've always considered "adding any significant manual complexity" to be a deal breaker for any change to dkp. That said, now that I'm not raiding and have my work stuff mostly settled, it's possible I have some spare time to work on things like this.

2) Offspec loot is something that's been considered many times, the main issue is that there were never very good ways to define "offspec" that didn't have overlap. The definition of offspec has to be "has near-zero benefit to your main spec". Any other definition breaks any dkp system. Offspec loot could never be allowed to creep past that definition, which is also a danger. As soon as people are able to start sneaking in items that are upgrades to their main spec for free just because other people passed on it, then you are fucked and added a whole new crazy metagame to loot distribution.

3) Decay and whether or not it's better than our current system is a very complicated issue that I haven't seen anyone here make a good analysis of, if you want something like this you need to compare how it changes our current loot distribution and make some kind of case for it improving the results significantly. Anecdotes don't count.