What needs to change is the notion that hosting your own web app, using open source software, involves uploading "scripts" to "web space". As long as this is the way 99% of hosting operates, PHP will maintain its prevalence. All the things going on with virtualized cloud hosting are key here. Move from the paradigm described above to where installing your own instance of, say, a blogging engine means uploading a complete VM image (or chef/puppet cookbook, or whatever) to your hosting provider, and open source developers are once again free to use their favourite technology. (Disclosure: I'm the author of Schnitzelpress, a tiny Ruby/Sinatra based blog engine that was mostly born as an experiment to find out how much of the above is possible today.)