Making an app though still isn't easy. Especially if you want to capture all the functionality of the forum.
You'd need at least two teams of people, one to expose the forum db as a RESTful web service API (assuming one isn't already there, though I think Tapatalk uses a similar API to interface with the forum) so that the app can make these calls to carry out functions such as creating posts, registering, replying, reporting, etc. The second team would work on the actual app, creating the UI and implementing calls to the API exposed by the RESTful web service.
Since there are a lot of functionality to be covered in development, plus ensuring security and no bugs means that a properly organized effort needs to be planned and executed. I don't think this would be good enough for a volunteer force of developers, especially with no centralized guidance and management.
That is why I think that contracting professional developers would be a much more feasible option in this case since they will deliver faster, fix the bugs and also provide future support for the app if needed.
Not saying that volunteers can't build the app. This is also doable, but this will definitely require someone with a lot of spare time on their hands.
