Because there are unaddressed items in this todo list:
The main issues here are xattrs and support for blocksize != pagesize.
I would consider both to be optional. We have various file systems
in tree that don't support either (e.g. JFS only supports 4K blocks
and OCFS2 doesn't support xattr) They shouldn't block merging.
2. Who will maintain this?
Currently there are two namesys employees working mostly on
enthusiasm. Divide them into 2 file systems, plus many people who
really help with fixing problems.
Merging will probably be a peak of work for the necessary changes,
then hopefully the work will be less once you're in tree because
you don't need to track mainline anymore
(assuming not to many bugs come in from users)