It also means that you now have a mechanism that will allow you to construct a string of packed integers that Perl has no way of unambiguously deconstructing.

I don't understand this at all.

This is what I mean:

$a = ''; $a .= chr 1<<$_ for 0..63;;

Dump $a;;
SV = PVMG(0x37b528) at 0x3058a0
  REFCNT = 1
  FLAGS = (SMG,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x3cb90f8 "\1\2\4\10\20 @\302\200\304\200\310\200\320\200\340\2
+40\200\341\200\200\342\200\200\344
...
\200"\0Malformed UTF-8 character (byte 0xfe) in subroutine entry 
Malformed UTF-8 character (byte 0xfe) in subroutine entry 
Malformed UTF-8 character (byte 0xfe) in subroutine entry 
Malformed UTF-8 character (byte 0xfe) in subroutine entry 
Malformed UTF-8 character (byte 0xfe) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
Malformed UTF-8 character (byte 0xff) in subroutine entry 
 [UTF8 "\x{1}\x{2}\x{4}\x{8}\x{10} 
     @\x{80}\x{100}\x{200}\x{400}\x{800}
     \x{1000}\x{2000}\x{4000}\x{8000}
     \x{10000}\x{20000}\x{40000}
  CUR = 504
  LEN = 512
  MAGIC = 0x3c856c8
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = -1

print join '-', map ord( chop $a ), 1 .. 64;;
0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-
+0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0
[download]

And:

$a = ''; $a .= chr 1<<$_ for 0..63;;

print length $a;;
64

$a = reverse $a;;
Malformed UTF-8 character (byte 0xfe) in reverse at (eval 47)

print length $a;;
75
[download]

If Perl can't handle it, it's a bug, not a feature. And not something I would concern myself with trying to handle.

Yet another, just another red herring.