Being forever backward-compatible is a curse that prevents innovation and makes you end up with the mess of a language that PHP is.
Re:PHP to deprecate MySQL extension
by pavel_lishin on Friday July 15, 2011 @04:08PM
(#2768866)
I agree, but you don't have to be backward-compatible forever - you can deprecate features gracefully.
Bonus points if you're not actually in control of the version of PHP your web app runs on.