what are the advantages with the Hurd over Linux, in general of course, nothing in depth

Flexibility for the user:

transparent ftp

$ cd /ftp://ftp.debian.org/debian
$ ls

personnal filesystem

$ dd < /dev/zero > myspace.img bs=1M count=1024
$ mke2fs myspace.img
$ settrans myspace /hurd/ext2fs myspace.img
$ cd myspace

Just curious, but I keep seeing these (and other similar) concepts being brought up as the amazing selling points of the Hurd, but all of this is entirely doable now in Linux with FUSE or things like it.

Nowadays, at LAST, yes, partly.

I'm not sure if an ftp filesystem has been implemented for FUSE yet, but its definately doable; and loopback filesystems like in your second example have been supported for years.

As a normal user? And establish a tap interface connected through ppp over ssh or whatever you could want to imagine?

What, then, are the major selling points or benefits?

These were just examples, Linux is trying to catch up in ugly ways indeed (yes, have a look at the details of fuse, it's deemed to be inefficient). In the Hurd, it's that way from the ground and there is no limitation like having to be root or ask for root to add magic lines, etc.