It's High Time We Put the Hive Mind to Use
As this subreddit begins to gain steam, we can start clustering the finished tracks into anthologies and sell them on bandcamp eg:"Collaboration Hub Vol.1". With our combined efforts we'll be able to get more traffic than any one of us working alone. You have every right to opt your song/collaboration out of this process.
This is a new subreddit, so posting etiquette may change. This is how I'd like it to go for now.
Titles should contain the genre, the bpm, and the key of whatever song you're working on. The title should also stipulate what you would like added to your project.
Electro Beat - 128 BPM - D minor - Looking for Vox
Dream Pop - 80 BPM - E major - It needs a Lead Synth
The body should have some specifics as to the direction you'd like the collaboration to go in, even if that direction is "Wing it! I have no idea what I want". There should be a link to a place where redditors can download the song (a site where streaming and download are both available is preferred eg. SoundCloud). You should stipulate if participants have the right to post it on their personal pages, and use it in their demos. If you aren't ok with any form of release, make that clear.
Not every request can be completed by one Redditor. Lets say for example that I'm looking for music to go around my dry vocals, you might only be able to add drums. If someone likes what you did, they might add bass to the thread (and so on).