Earlier quoted context omitted.
Why do you think that MediaWiki is not optimized to handle thousands request per second just because it is written in PHP? MediaWiki repository size is about 1.4 GB and according to phploc it has closer to a million lines of PHP code. Sounds like fools errand to rewrite it.
I looked into the topic in some detail year ago, because I copied Wikipedia's approach for an in-house CMS editor. I looked through the code, did loads of performance experiments, read through related forums posts, etc... The wiki staff themselves admitted that the current parser is inefficient, partly because of PHP, partly because the underlying grammar was not designed to be efficient, and partly because the parse…
You can parse grammar on save and make an optimized compiled format where static content is already resolved. Next step is to substitute semi-static content (like author name) to a runtime format, this last format can handle dynamic data substitution like current date & time, but probably going to be rare that any substitution is needed for the runtime format (how much truly dynamic data does a wiki have?), most of the time just print it with readfile or similar. Only difficult part here is cache invalidation for the runtime format (I know, it is one of the three difficult things you can do in programming).
3000 request/second in PHP is not hard, especially if you plan for it.