As far as stackoverflow is concerned, many questions now-a-days, I see are related to php. Why cannot a seperate stackexchange site be opened especially for php enthusiasts. It would really be helpful for programmers to find a dedicated website for php. Also it will become a powerful learning hub in terms of open source
Your thinking seems a bit backwards. Stack Overflow is the most successful, most popular site for programmers. It is about the 50th largest site on the web. With over a half million PHP questions on Stack Overflow, it has also become the best resource for PHP users.
So what you are asking is to now remove PHP questions from that site — making Stack Overflow <quote>"the number one site for programming questions… except for PHP."</unquote>
That doesn't make sense, and you're going to have a tough case showing that it's somehow better for the PHP community.