(Post below has been heavily edited after I made further progress.)
If you didn't know, sgrogan and I (with precious help from f3nix and welcome advice from blacey on git usage) have been working on resuming updates on the Daily Builds PPA. Our progress has been detailed in the Ubuntu PPA Maintenance Coordination topic.
With the current master bringing huge changes to the PartDesign workbench along with quite a few bugs (and possibly incompatibilities with other workbenches?), we've figured that we should allow users to install both versions on their system: the 0.16.670x release from the Stable Releases PPA as well as the freecad package from the Daily Builds PPA.
This requires that we rename the daily build package. We've settled on "freecad-daily". I believe I have it working now.
One thing we cannot avoid: existing users of the Daily Builds PPA will have to install a new package named freecad-daily. I don't see how we can automate it being installed through updates.
I've had another idea: would it be desirable to force installation of the freecad 0.16.6703 package along with the freecad-daily one? I think it's possible now.
Or should we allow Daily PPA users to only use the development version?
Odd things may happen with two different FreeCAD versions installed on the system. For example, if one is to double-click on a FreeCAD file, which version will launch? It may be possible to right-click and choose "Select with" and select either version.
Another thing that I'm not sure about is if we should create two separate ~./FreeCAD folders. This would mean that user preferences would be set separately in each version. Add-on Mods would need to be installed in each folder (unless the user creates a symlink).
Your thoughts are welcome.