I'm not good (another area where I lack knowledge :( ) in streams and related. But this would be good if a group of experts can work on deciding whether flow should be pushed into squeak. In the past I heard (I do not remember quite well) that flow was quite large and really changing a lot of stuff in a non-compatible way with a limited transition path.
Modularity, Namespaces and compatibility layers seem like the (only) way forward
This approach would also give the structure for compatibility with mainstream (and/or other dialects of) Smalltalk.
Probably a lot of work, although most likely worth it in the end.
Aaron