The cross-platform requirements are the most difficult. If Phish were to be a cross-platform application, we would need to be very careful about how images are rendered, and how much we relied on any specific application framework. We would want to generalize our approach to threads and take advantage of cross-platform collection classes such as the STL. The requirement that the product be cross platform will slow our time to market, but in exchange, we'll have a more flexible product.
I propose we design for cross-platform, but implement the first version within the MFC framework. This will significantly simplify the work and will shorten the time to market. We'll note those areas of the design which are most dependent on the MFC and which we'll want to break out with a layer of abstraction, so that migrating to another application framework, or to another platform, will be easier.