Welp... let's try looking at all the main factors...
-Since Newgrounds has been a little tame on the contest front, a lot of unofficial ones have popped up. As much as I'd like to join all of them, my workflow just won't permit it. I'm sure a few others are like that. When it comes down to the audio forum regs, a few is actually a lot. As great of an idea as it is, I'm sure most of us are bogged.
-Overkill. I've said it before and I'll say it again. Everyone is/was already talking about MJ's death. There are plenty of sources for everything MJ related. I've already talked to my entire family about it. As appropriate as it would normally be for the death of a musician to be discussed in an audio forum, it's already been brought up everywhere else. That makes anything we could say in here spam. Unless someone wants to talk about the chord structure to a said song in here but that takes away from the competitive nature of a contest in the first place.
-How do you expect us to get the a cappella? As good as some of us might be at mixing, I really doubt anyone wants to take the time to try and manually extract the vocals from a mix for other people. It takes time, it takes skill and it takes genuine selfless effort... unless you know of a place that's selling the a cappella. In which case I have only to ask where the selflessness is...
Don't get me wrong, it's a great idea but those three factors make it all seem unlikely.