I agree with Avi. So please think about transition.
Flow is A Good Thing. As always, the hard part is persuading a large group of people to adopt something new, especially since it is a replacement not an add on. I don't see any particular problem with replacing all the prims, especially since they're in plugin(s) but getting package owners to rewrite to use new streams and so on.... I've never been able to think of a way round that part.
I've advocated this in the past without any success, but I might as well try again: the way to get people to adopt Flow is to make it possible for them to use it side by side with the existing streams, so that they can migrate to it incrementally without anything needing to be broken during the process. All this means, I think, is prefixing Flow's classes so that they can coexist in the image with the old Stream implementation. Yes, there's something aesthetically unpleasing about having FlowStream or FStream instead of just Stream, but if adoption is actually a goal it seems a small price to pay.
Avi