I've been making progress on ext4fs driver for OpenBSD current, after upgrading and messing with CVS directories a couple of times I've updated the code to read block descriptor groups so now mounting my test ext4fs partition into /mnt works and listing the parent directory / gives proper info on /mnt so lstat on root inode works !
Now I'm having panics and don't really know what to do so if you want to help out please reach out.
See the progress on Github.