Aquí hay una lista de los cambios que se introducirán en PHP6,  (vía)

• FILE_BINARY and FILE_TEXT constants available for use with filesystem functions.
• register_globals will be gone.
• magic_quotes will also disappear.
• $HTTP_*_VARS has been removed, in favour for $_GET, $_POST, etc.
• ereg() no longer available in core PHP6.
• Initiating objects with the reference operator (& new Object()) will generate E_STRICT error.
• E_STRICT error messages are included in E_ALL errors.
• {} for string offsets no longer available.
• [] un-deprecated for accessing characters in a string.
• ASP-style tags can no longer be used.
• Better Unicode Support.
• var will be an alias of public, and raises E_STRICT warning.
• Support for 64 bit integers.
• With ternary operator, the “true” expression is no longer required – this can be done: $a = $s ?: ‘b’; (Not clear yet exactly how this will work).
• zend.ze1_compatibility_mode removed.
• safe_mode is being removed.
• Freetype1 and GD1 support removed.
• dl() is only enabled when a SAPI layers registers it explicitly.
• Support for dynamic break levels removed.
• XMLReader and XMLWriter will be in the core distribution.
• mime_magic removed from the core.
• Fileinfo moved to the core.
• ext/soap on by default.
• foreach supports multi-dimensional arrays: foreach($a as $b => list($c, $d))
• microtime() will return as float by default.
• opcode cache included in core distribution, but turned off by default.
• flags parameter available for file_get_contents().
• before_needle parameter added to strstr() – allows strstr() to return part of haystack before occurence of the needle.
• namespace, import, and goto become reserved words.

Me parece que la dirección que está tomando PHP es la mejor; PHP se ha caracterizado por ser un lenguaje fácil de usar y aprender para los novatos pero al mismo tiempo un lenguaje poderoso y flexible para los más experimentados y estos cambios están enfocados precisamente para sacarle mayor provecho al poder de PHP.