Thanks to the hard work of some devs in the ecosystem, who are working on actual projects (plus me, who hasn’t done much coding in the past few years but can bluff my way through stuff), I present:
The Holochain RSM Migration Guide!!! 
Thanks to @guillemcordoba who got the ball rolling, @tats_sato who made valuable contributions and insights, @Connoropolous who reviewed it with his keen eyes, and the whole core dev team who continue to build Holochain RSM and explain it to the world.
This guide is meant to be an exhaustive list of all the deltas between Holochain Redux and RSM, which we hope will speed up your efforts to migrate your hApp. We don’t expect that it’s exhaustive just yet (I caught one important omission post-publishing), so we encourage you to contribute your own learnings. The best way to do that is to fork the holochain-open-dev/blog repo on GitHub and submit your additions/changes as a pull request.