diffoscope doesn't indicate guestfs support is missing, even when guestfs could help diff a binary.

Given a file beginning like:

00000000: eb3c 906d 6b66 732e 6661 7400 0204 0400  .<.mkfs.fat.....
00000010: 0200 0200 a0f8 2800 2000 4000 0000 0000  ......(. .@.....
00000020: 0000 0000 8000 2978 5634 1245 4649 424f  ......)xV4.EFIBO
00000030: 4f54 2020 2020 4641 5431 3620 2020 0e1f  OT    FAT16   ..
00000040: be5b 7cac 22c0 740b 56b4 0ebb 0700 cd10  .[|.".t.V.......
00000050: 5eeb f032 e4cd 16cd 19eb fe54 6869 7320  ^..2.......This 
00000060: 6973 206e 6f74 2061 2062 6f6f 7461 626c  is not a bootabl
00000070: 6520 6469 736b 2e20 2050 6c65 6173 6520  e disk.  Please 
00000080: 696e 7365 7274 2061 2062 6f6f 7461 626c  insert a bootabl
00000090: 6520 666c 6f70 7079 2061 6e64 0d0a 7072  e floppy and..pr
000000a0: 6573 7320 616e 7920 6b65 7920 746f 2074  ess any key to t
000000b0: 7279 2061 6761 696e 202e 2e2e 200d 0a00  ry again ... ...
000000c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................

And the fsimage support of https://salsa.debian.org/reproducible-builds/diffoscope/blob/master/diffoscope/comparators/fsimage.py#L87-97

diffoscope printed:

diffoscope.comparators.utils.specialize: File not identified by any comparator.

Note, file reported:

DOS/MBR boot sector, code offset 0x3c+2, OEM-ID "mkfs.fat", sectors/cluster 4, reserved sectors 4, root entries 512, sectors 40960 (volumes <=32 MB), Media descriptor 0xf8, sectors/FAT 40, sectors/track 32, heads 64, serial number 0x12345678, label: "EFIBOOT    ", FAT (16 bit)

IT would be really super if diffoscope noted that guestfs support is missing, and could provide a better diff.