Hi @Karl,
We are actually in the fortunate position that the same people that work on the Objective-C framework at Apple are also highly involved with the open source project. This includes new code contributions, code review approvals and comments on GitHub, forum posts and more. We are all very interested in moving both projects forward and are very receptive to ideas from the community. We can discuss those ideas here. When there is overlap with open source work and new API (as there has been for things like Codable support in Foundation), there is an opportunity to participate in both the review and the implementation.
The file handle and scanner improvements I mentioned are a direct result of the work on swift-corelibs-foundation and community feedback. We have also experimented with asking for targeted API enhancements in cooperation with the community (e.g. RFP: Ordered Set), although I admit that hasn't moved forward at the pace I would like.