I'm new to the world of collabs, and have only tried starting a couple, and (I think) succeeded with one. I think the fact that the one I asked two other participants to do with me will work out best (fingers crossed for their videos this week), because we are all involved with cooking, and the discussion we had about it worked out really well.
I did have a couple of people who reached out to me for collab material, which I dutifully shot and sent to them, and so far...nothing. I would love to participate with them (they have fewer subscribers than me, so it's not a case of wanting to grab a huge audience, I just like the community aspect of it), but I won't pester anyone beyond the first reminder email that I need their video segment and would love to see what I shot in their videos. But it's a roll of the dice...nobody owes you anything when it comes to YouTube, so it's not something that I'm going to worry about too much. It wasn't a huge time commitment to shoot inserts for those projects that are still in the air.