If you want to get rid of PHP, keep it conceptually simple. Mircea said that Python or Ruby are alternatives - they are not. Non-programmer people would need to learn about classes and objects*, and about how a good web app generates HTML in at least two steps** and how to map*** tables to objects (that they have not yet understood) and what are modules and why they are important and...
Or, well, one can start with PHP, learn how to do a "Hello, World" in two minutes and save some data in MySQL in ten minutes.
I am a Java programmer at work (could be no more corporate-y) and a Python developer in my projects (could be no more hipster) but I admire PHP and its ability of solving problems. It grows because, some times, some poor soul wants to create an online encyclopaedia, or some teacher needs an online teaching platform, or someone wants to write a blog. Those people do not want to learn to program, they want to solve problems.
I thing most projects to defeat PHP are doomed because programmers got it wrong. PHP is not in the same league of Python, C#, Ruby, Java or whatever. PHP is more like Excel, a not-so-beautiful tool for helping laymen to solve problems with a computer. And you know what? I like spreadsheets, although they are extremely shitty from a programmers perspective (PROCV() anyone)?
Paulmorriss proposes to write an alternative to Wordpress. Nice! After that, create an alternative to Mediawiki, Moodle and OpenCart as well. Oh, and do not forget: they should be useful, stable and easy! Now, let me tell my history: I was a fiercely advocate for Linux in my undergraduate days. I was always pointing how it was more stable and secure. What used to happen is that people kept asking me how to, let us say, edit MS Office documents or running AutoCAD or using Photoshop. With some time, various open source projects created solution to it. I liked it because I am an Ubuntu user and I need these applications, but for the common people from windows, they are lame clones for something they already need. Also, if they needed some application, they could hack it with Visual Basic or Delphi, while they would start learning about autotools(!!!) in Linux. All these alternatives people created, as great as they are, just did not solve the real, bigger problem, that is to empower non-programmers. It does not matter how many alternatives to real applications in PHP you create - the poor user will stay disenfranchised if not using PHP.
So, this is it. If you want to ban PHP, create a new as-easy-as-Excel tool for the web. It will be ugly, because those tools are aimed to little problems, but do not delude yourself that people out there care about the "elegance" of your language. Everything our favorite languages has was put there to satisfy us, not PHP users. If we want to win, we need to unlearn.
But do we want to create another unlearned tool?
* And man! I was a C programmer and it took me some two years to get it
** First, generate the data, then pass it to a template engine.
*** Every time you say the word "map", you can count on your layman listener getting lost. This is hard mathematical stuff, you just forgot it because you are used to it