This will probably trigger a lot of opinionated answers which, in this case, may not be so bad. Here's mine.
In general I would say yes, 40 contributors for a proprietary application is a lot. By the time you have this many contributors you'd better be sure to have a lot of safety measures in place that limit the room for individuals to do their own thing. In that regard I agree with Michael. My main concern would be control of design issues, making sure things do not get off the rails. You will need a gate keeper, someone familiar with the overall design who is in control of what goes and what not. He will grow to trust a couple of individuals down the pyramid, a pyramid that will have to grow steadily. Then it can work. You do not want groups of people developing stuff independently from each other where each group is unaware of what other groups are doing.
The more people come in, the more management this will require. It takes time for things to settle in and for people to become effective, like in any organization. Just starting a project and throw 40 people at it immediately is not likely to succeed. So yes, it can work but only if you start small and take it one step at a time.
I do not believe is shared responsibility so I say you will need a pretty rigid hierarchy, a technical owner to rule all contributions. If you do not have this you will either get chaos or the inability to make big changes when needed.