Last night I spent about an hour removing code from Time::Piece and adding @ISA = DateTime... Results so far:
$ make test
cp Seconds.pm blib/lib/Time/Seconds.pm
Skip blib/lib/Time/Piece.pm (unchanged)
PERL_DL_NONLAZY=1 /usr/bin/perl -Iblib/arch -Iblib/lib -I/System/Library/Perl/darwin -I/System/Library/Perl -e 'use Test::Harness qw(&runtests $verbose); $verbose=0; runtests @ARGV;' t/*.t
t/01base........ok
t/02core........NOK 24isdst Not yet implemented at blib/lib/Time/Piece.pm line 161.
t/02core........NOK 25isdst Not yet implemented at blib/lib/Time/Piece.pm line 161.
t/02core........NOK 89isdst Not yet implemented at blib/lib/Time/Piece.pm line 161.
t/02core........FAILED tests 15, 17-21, 23-26, 33-34, 36, 41, 44-45, 50-52, 60, 64, 66-68, 72, 78, 80-91
Failed 38/91 tests, 58.24% okay
t/03compare.....ok
t/04mjd.........ok
t/05overload....ok
Failed Test Stat Wstat Total Fail Failed List of Failed
-------------------------------------------------------------------------------
t/02core.t 91 38 41.76% 15 17-21 23-26 33-34 36 41 44-45 50-
52 60 64 66-68 72 78 80-91
Failed 1/5 test scripts, 80.00% okay. 38/113 subtests failed, 66.37% okay.
make: *** [test_dynamic] Error 35
Not bad for an hour's worth of hacking