Updates:
There are now some blog articles 
about this work:
- https://hackaday.com/2020/04/14/altium-has-its-2kicad-moment/
- https://www.cnx-software.com/2020/04/05/how-to-build-kicad-on-ubuntu-18-04-and-import-altium-pcb-files/#importing-altium-pcb-layout-in-kicad
- https://blog.oshpark.com/2020/04/05/altium-board-importer-for-kicad/
Two MR with bugfixes and improvements:
-
https://gitlab.com/kicad/code/kicad/-/merge_requests/147
- fix coverty issues, improve code style
- support more altium layers which are stored as string
-
https://gitlab.com/kicad/code/kicad/-/merge_requests/151
- improve code
- fix crasher bug due to coding error
- add support for new string replacements (New string replacement options for kicad assets)
The most annoying bugs I need to fix next, are for now:
- some weired pads in some boards, which should be not on non-copper?!?? Please give in your experience if you know how Altium does this
- improve zone handling in planes as well as fills in keepouts