Уже некоторое время известно какие несовместимые изменения будут в Perl'е 5.28. Вот они:
Incompatible Changes
Comma-less variable lists in formats are no longer allowed
Omitting the commas between variables passed to formats is no longer
allowed. This has been deprecated since Perl 5.000.
The ":locked" and ":unique" attributes have been removed
These have been no-ops and deprecated since Perl 5.12 and 5.10,
respectively.
"\N{}" with nothing between the braces is now illegal.
This has been deprecated since Perl 5.24.
Opening the same symbol as both a file and directory handle is no longer
allowed
Using "open()" and "opendir()" to associate both a filehandle and a
dirhandle to the same symbol (glob or scalar) has been deprecated since
Perl 5.10.
Use of bare "<<" to mean "<<""" is no longer allowed
Use of a bare terminator has been deprecated since Perl 5.000.
Setting $/ to a reference to a non-positive integer no longer allowed
This used to work like setting it to "undef", but has been deprecated
since Perl 5.20.
Unicode code points with values exceeding "IV_MAX" are now fatal.
This was deprecated since Perl 5.24.
"B::OP::terse" no longer exists.
Use "B::Concise::b_terse" instead.
Use of inherited AUTOLOAD for non-methods is no longer allowed.
This was deprecated in Perl 5.004.
Use of strings with code points over 0xFF is not allowed for bitwise string
operators
Code points over 0xFF do not make sense for bitwise operators.
Setting "${^ENCODING}" to a defined value is now illegal
This has been deprecated since Perl 5.22 and a no-op since Perl 5.26.
Backslash no longer escapes colon in PATH for the -S switch
Previously the "-S" switch incorrectly treated backslash ("\") as an
escape for colon when traversing the "PATH" environment variable.
[perl #129183]
the -DH (DEBUG_H) misfeature has been removed
On a perl built with debugging support, the "H" flag to the "-D"
debugging option has been removed. This was supposed to dump hash
values, but has been broken for many years.
Use of strings with code points over 0xFF is not allowed for bitwise string
operators
Code points over 0xFF do not make sense for bitwise operators.
Что же касается выпиливания ENCODING, то всё и так работает с любой локалью автоматически. А для улучшенной поддержки конкретно KOI8-R есть модуль Char-KOI8R от японца по имени INABA Hitoshi.
