One question: why do you feel PHP is heading toward obsolescence? I've seen others mention this and am not sure what they mean.
PHP exists to script web pages. It’s been expanded to allow you do a lot of stuff from other application layers, but it basically still serves that one layer. A key advantage is that it has a nice, shallow learning curve. And, as the backbone of Joomla, Drupal, etc., it ain’t going anywhere any time soon.
Perl is the former language of choice for doing some of the nitty-gritty web-development tasks that PHP isn’t particularly well suited for, but it was never terribly good for scripting web pages; it’s very easy to build highly idiosyncratic code which is undecipherable to all but the top programmers. Essentially, once you convince someone to allow you to develop a system in Perl, you have a job for life. And a lot of users of such code don’t exactly enjoy that feature.
Python is replacing Perl, but it also does what PHP does easily enough that there seems little reason to use both Python and PHP for one enterprise... except the vast arrays of PHP creations.