Also, a major part of needing to predeclare your variables is to avoid typos. Having default-lexical scope avoids a lot of the nasty action-at-a-distance that default-global scope produces, but it still can't detect the typo between $outfile and $out_file for you, which I consider the major point of using strict.

:) I was going to list this as a reason, but I remembered warnings

$ perl -Mwarnings -e " $foo = 1; "
Name "main::foo" used only once: possible typo at -e line 1.

$ perl -Mwarnings -e " my $foo = 1; "
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If warnings can detect this I see no reason a New pragma 'scope' to change Perl's default scoping couldn't do the same

Naturally that won't help if you're making the typo twice, but neither does strict/my :)

Yes, but turning a single use of a lexical variable into a warning will raise warnings for code like:

use Guard;
sub foo {
    $guard = scope_guard { print "done\n" };
    ... do stuff, without ever mentioning $guard again ...
};
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This could maybe circumvented by only raising the warning when my is missing:

use Guard;
sub foo {
    # This will warn
    $guard = scope_guard { print "done\n" };
    ... do stuff, without ever mentioning $guard again ...
};
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Detecting this will be tricky, but it should catch most of the typos that would get a warning.