I have a few improvement ideas for the publishing process. One is already covered here: rapid rollback
Here a few more:
in DTM it was sometimes a bit annoying that a saved rule was directly visible on staging. But now that we have a proper workflow I would like that feature back for libraries that are only built for development. So, as long a library hasn't moved to the approval stage, I see a flag "always use latest" which indicates that the latest version of any extension, data element and rule within the library will be used. So no new revision while you are still developing and debugging the rules for a new property or an overhaul of an existing one. This would integrate well with the "Working Library" select on the upper right. So if you edit a rule, save and build the library that uses it and has the flag set.
Have a diff available like in DTM, but maybe let the user choose what revisions to compare to each other with "latest" as also an option.
If a build fails have some error log available for the user to see why it failed (I had a few failed builds yesterday which seem to have been because of the server having problems, and not my library, as I was able to build it without changes today).
Build the same library for multiple development environments. I have multiple development environments (like a continuous integration server and my local development instance) and it would be cool to be able to build the same lib for both while in development. Launch supports multiple development environment configurations, so it wouldn't be too far fetched.