All this even though most PHP4 scripts run unaltered in php5.
And now you suggest to drop backwards compatibiliy to get rid of warts? How long do you think it would take before that new language will get any significant deployment? What good will all the new features be if you are not able to use them in the next 10+ years?
Personally, I like to see them add features in a backwards compatible way. Knowing PHP and programming in general, I can stay away of the bad parts but still use all the new features in the foreseeable (2-3 years) future.
Just have a look at python3 of you want a taste if what you were just suggesting.