You can! All of those filesystems you mentioned were created by people, and you can do it just the same way. It is, however, quite a lot of work to get something as good as any of those, let alone better. You've also hit on one of the problems - nothing else is going to support your filesystem.
If you're interested in trying anyway, just out of curiosity, do a little research into FUSE, Filesystem in Userspace. FUSE is a tool that lets you write a filesystem without needing to integrate with the very low-level parts of the operating system, which takes some burden off of your implementation.
You can! All of those filesystems you mentioned were created by people, and you can do it just the same way. It is, however, quite a lot of work to get something as good as any of those, let alone better. You've also hit on one of the problems - nothing else is going to support your filesystem.
If you're interested in trying anyway, just out of curiosity, do a little research into FUSE, Filesystem in Userspace. FUSE is a tool that lets you write a filesystem without needing to integrate with the very low-level parts of the operating system, which takes some burden off of your implementation.