PHP interpreters are very common, but the PHP syntax & libraries are inconsistent & cumbersome (IMO, of course). I think a language that compiles into PHP but provides higher level level features (like, modules, mixins, list comprehensions, etc...) and easier syntax (like optional semicolons, implied returns, no dollar sign for variables, optional brackets and braces, etc...) would be valuable. Does anything like this exist?
.php files. On your own servers, if you don't like PHP, you can just use Ruby, Python, Perl, or any of the myriad JVM or .NET languages.
All of that said, it could be cool to have a language that's like CoffeeScript for PHP. The ongoing success of WordPress, and its use on servers that users often have little control over, attests to PHP's unique place as a deployed language. It's also difficult to use PHP with alternative markup languages like Haml. Perhaps an alternative markup language combined with a fresh PHP syntax could produce a compelling enough reason for people to precompile their PHP.