I've been making proposals to developers to work together for a very long time. I do it very often. I know they don't think highly of people who make offers to work with them. I know this because they usually don't even bother to respond.
The ridiculousness of this came home to me in 1989 when I proposed adding a feature to MORE to the people at the company I founded. They asked me to explain how this would increase sales of the product. I groaned. Maybe it won't increase sales of the product. But as a user, I need it! Do I have to re-implement the whole app to get this one feature. Silence. Yes. And I did re-implement the whole product. All for the want of a single feature.
I did write the original version of the software that became MORE, but that was a few years before I needed the feature, and by then I was off working in a different direction. I needed exactly what MORE did, with hooks so it could be part of my editorial system. I couldn't explain to them how it would all fit together because I didn't know, and because I was working in an area of publishing that they had never explored. I knew this, because almost all the people there used to work for me.
People will also say I should have asked for the source for WordPress in the example below. It already is open source. But that was even more inaccessible to me. It was actually easier to write a new blogging platform than to figure out how to hack the feauter I needed into WordPress.
Zooming forward in time, it happened when I asked the WordPress guys to add a feature that would allow me to store the XML source text of a post alongside the HTML rendering. No. I don't think they thought about it much. I had to spend a half-year implementing a new blogging tool just so I could have this feature.
An editor of a great magazine envied my River. I said great, let's do one for you. I'll do the work for nothing, you just have to rent an EC2 server for $90 a month. This is a publication with a hundred employees, at least some of whom have expense accounts. One lunch for one of these people might cost $90 if they took someone with them. Okay maybe two lunches. But they would get a new editorial product and a chance to move the art of magazines on the web forward. They would at least get a few articles from it.
I keep making proposals, knowing that it's going to hurt a bit, in some ways to be turned down for such stupid reasons. I think the problem is that in most people's minds their support is meaningless. They need other people to recognize them in order for them to get ahead. But one sure-fire way to get someone to work with you is to say "Yes" when they ask if you want to work with them.
I'm not saying you can work with everyone. But in the cases above, I was hardly a random person off the street. I had a track record with each of them, a reputation. I thought I had their respect too (which means they would listen).
I read a tweet from Susie Wee, an exec at Cisco who is very much a Yes kind of person, that quoted hockey great Wayne Gretzky who said "You miss 100% of the shots you don't take." I thought that was profound (and righteous).