Until now it has been possible to handle the same project with both 5.1 and nightly builds provided that you manually deleted “max_error” line from the pcb file which was put there by the nightly builds. Some new features are incompatible (chamfered pads, hatched zone filling) but if you don’t use them they don’t affect files.
Now it looks like the branches will soon diverge too much to be even semi-compatible. See https://lists.launchpad.net/kicad-developers/msg41324.html.
It would be nice if KiCad had some kind of input filter and log errors during file read for non-supported features. This would make the file reads more robust.
@seth suggested an ‘incompatibility report’ for issues like this on the developers forum - https://lists.launchpad.net/kicad-developers/msg41078.html - which sounds like a good idea.
The minimum required C++ version for the compiler has been set to C++14. If you have a system (which is still supported by its makers) with only a C++11 you can tell the developers in the mailing list, but only the platforms which are offcially supported by KiCad are supported 
If you have a build system set up but haven’t compiled for a while, now is the time.
Has anyone considered versioning all paths so multiple versions can be installed at the same time? I’d like to experiment with the nightlies but don’t want it to impact my v5 installations.
What’s the easiest platform to build kicad on? I’ve tried the osx build scripts (https://github.com/KiCad/kicad-mac-builder) many times on different code bases, but never managed to build it, or if I hacked the scripts/cmakefiles to finish they wouldn’t produce anything that worked. (Read: didn’t immediately segfault.)
Yes, see Running several KiCad versions on the same Windows machine.
Please open a new thread for this, it’s a larger topic.
Pcbnew -> Inspect -> Show Board Statistics
Nice!
It would be also useful to have a list/check of annular rings
It has been several years since a PCB fab charged me per via.
What would be useful would be a simple summary of drill sizes used.
A nice idea, can you also post an example of the generated report file ?
Another vendor includes Track Lengths Routed and an Unrouted Count / rats nest length total, and those can be useful for sign-offs.
The version numbering of the nightly builds will probably change soon, see https://lists.launchpad.net/kicad-developers/msg41939.html.
New version number for development builds will be 5.99 to make clear that it’s later than 5.1. As of now they have been numbered misleadingly as 5.0.xxxx-gxxxx…
EDIT: some time ago they were identified as 6.0 which also was misleading, maybe even more so.
New eeschema selection highlighting.
Browse button in Sheet Properties dialog.
Filters in Footprint Browser.
Control over 3D Model updating in Update Footprints and Change Footprints.
Preference for whether Flipping a footprint to the back of the board flips it top/bottom or left/right.
Undo/redo while editing schematic text objects.
Could this be cherry picked to 5.1 nightly?
Sadly, no. 5.1 doesn’t really have selections at all, depending instead on block commands and a “current item”. 6.0 Eeschema is based on the modern toolset from Pcbnew, with a first-class selection model.
No prob. Thanks 
…
Jp charras is working on a board stack-up manager. It’s not in the master branch yet but should be quite soon. Here’s a screenshot or two (self-compiled on Linux with patch):
Paste Special lets you keep schematic annotations in copied symbols when pasting.
(@JeffYoung, the checkboxes should be changed to radiobuttons because they are exclusive.)
Will this also affect the 3D visualization and the File>>Export models?
