I think 20% time is naturally opposed to collaboration.
In my head, "20% time" is actually "work on what I want to work on", and I spend all week working on things someone else tells me to do. If I take some "me time", it's not going to be used for someone else. And if I'm going to do something for someone else, I'm going to just get my regular projects done.
There's a small possibility that someone else has a great idea that I really want to help with, but that idea would have to be big enough that 2 people could work on it at the same time, too.
So in the end, I think 20% Collab is a bit of an oxymoron.
In my head, "20% time" is actually "work on what I want to work on", and I spend all week working on things someone else tells me to do. If I take some "me time", it's not going to be used for someone else. And if I'm going to do something for someone else, I'm going to just get my regular projects done.
There's a small possibility that someone else has a great idea that I really want to help with, but that idea would have to be big enough that 2 people could work on it at the same time, too.
So in the end, I think 20% Collab is a bit of an oxymoron.