You don't need a Stackexchange site for this. You can use existing technology to create similar functionality.

Suppose I update my user page to include current projects. I can add a section which states open problems I am interested in sharing, along with links I consider relevant.

However, I can do more. I can create multiple accounts, each with their user page, which contains the set of open problems, relevant links to more information, and a contact email for correspondence/maintenance purposes.

I can do more with this. Any relevant MathOverflow question I can attach as a favorite to that user. I can have that user post an answer to a relevant question which answers the question and highlights the closely related open problem. It is against site policy to use such accounts for. lying purposes, but messaging to and from accounts can be used to end more data toward that account related to the open problem. One now has a favorites page and an all actions page which can be harvested for information. If everybody created an open problem account for their open problem and used it responsibly, you would get a lot of relevant information quickly that could be searched with Google restricted to MathOverflow/users.

I don't think a specialized exchange site is needed, just a creative use of the existing system.

Gerhard "Get Use Out Of Users" Paseman, 2019.05.19.

You don't need a Stackexchange site for this. You can use existing technology to create similar functionality.

Suppose I update my user page to include current projects. I can add a section which states open problems I am interested in sharing, along with links I consider relevant.

However, I can do more. I can create multiple accounts, each with their user page, which contains the set of open problems, relevant links to more information, and a contact email for correspondence/maintenance purposes.

I can do more with this. Any relevant MathOverflow question I can attach as a favorite to that user. I can have that user post an answer to a relevant question which answers the question and highlights the closely related open problem. It is against site policy to use such accounts for voting purposes, but messaging to and from accounts can be used to send more data toward that account related to the open problem. One now has a favorites page and an all actions page which can be harvested for information. If everybody created an open problem account for their open problem and used it responsibly, you would get a lot of relevant information quickly that could be searched with Google restricted to MathOverflow/users.

I don't think a specialized exchange site is needed, just a creative use of the existing system.

Gerhard "Get Use Out Of Users" Paseman, 2019.05.19.