It will be good if we can find a way to avoid reinventing the wheel.
I tought that having a clear way to do the transition to oficial will be a good idea to share (and release) modules in beta status for testing while they do not reach the requirements for beeing oficial. The apache incubator projects is an example of such workflow. For example, we may contribute the WooCommerce connector for Tryton as incubator module and there if enought interest on it finish to make it an official module. Also this will allow some people to start a module and allow others work to make it become official.
I think the may benefit of unoffical module is to publishing them on some place so anyone can contribute it. So we should care at least to remove unmaintanined modules or to not release them. So we must carefully think on which release proces to use and when to deprecate such modules.
I do not dislike the idea but we should define the rules for everyone and find if it is really interest on it. I guess a lot of people will say thats interesting but less will contribute, so we need to give contributors some benefit to attract them.