I think you will find "file length" limit refers to exactly that, the file length. Anyone that uses SFS knows that 100 character file names are not a problem (except with my old (commercial) copy of Dopus 4). IIRC the SFS docs say that they limited the filenames to 100 chars because of dos.library;
SFS docs:
- Fast reading of directories.
- Fast seeking, even in extremely large files.
- Blocksizes of 512 bytes up to 32768 bytes (32 kB) are supported.
- Supports large partitions. The limit is about 2000 GB, but it can be more depending on the blocksize.
Support for partitions larger than 4 GB or partitions located (partially) beyond the 4 GB barrier on your drive. There is support for New Style Devices (NSD) which support 64 bit access, the 64-bit trackdisk commands and SCSI direct.
- The length of file and directory names is internally limited only by blocksize. Limitations in the dos.library however will reduce the effective length of file and directory names to about 100 characters.
- The size of a file in bytes is limited to slightly less than 4 GB. Because of limitations in dos.library we will however probably not allow files larger than 2 GB, to avoid potential problems.
So... a new FFS system should be able to match/exceed these specs, since they ARE playing with actual Amiga source code

Cheers,
- Paul