[Note the Reply-To.]

   That's another issue; it's clearly a bug for the filesystem type to
   override the ability of the system to try* to mount a device.  Unix has
   historically given one rope enough to hang oneself with; I personally
   mind not being able to just say "look, I know it doesn't *say* it's a
   ufs filesystem, but believe you me, it is."

That depends.  I tend to agree with this, but only for file systems.
For swap partitions, the kernel now *requires* that the partition type
be FS_SWAP, to avoid accidents.