A small update to the BFS incompatibility: I've now ported the original logging structure to the R5 version of BFS as well, so that the tools like bfs_shell can now successfully mount "dirty" volumes, too. I also found another bug in Be's implementation, and needed to cut down the log entry array by one to make it work with larger transactions.
Now I am working on implementing sub transactions. If you have tried out Haiku and compiled some stuff or just redirected some shell output to a file, you undoubtedly are aware that this takes ages on the current system.