Couldn't there be some way to mark a 'bundle' file and use that mark to discriminate between where multiple namespaces are or are not allowed in zend_compile.c? That would eliminate the potential for abuse, no?
Not really. People would start "bundling" files left and right, just because somebody on the list said it's so much faster, and any mark can be set by anybody.
That depends on how many 'bundle files' are allowed. I hate to say it, but if this were an INI directive rather than a keyword it would be possible to limit bundling to a single file, or to any given number.
/me waits for the sky to fall on her head