i.e to replace Apache with a PHP application that sent back html files when http requests for .php files are sent?
How practical is this?
It's already been done but if you want to know how practical it is, then i suggest you install and test with Apache bench to see the results:
http://nanoweb.si.kz/
Edit, A benchmark from the site:
Server Software: aEGiS_nanoweb/2.0.1-dev
Server Hostname: si.kz
Server Port: 80
Document Path: /six.gif
Document Length: 28352 bytes
Concurrency Level: 20
Time taken for tests: 3.123 seconds
Complete requests: 500
Failed requests: 0
Broken pipe errors: 0
Keep-Alive requests: 497
Total transferred: 14496686 bytes
HTML transferred: 14337322 bytes
Requests per second: 160.10 [#/sec] (mean)
Time per request: 124.92 [ms] (mean)
Time per request: 6.25 [ms] (mean, across all concurrent requests)
Transfer rate: 4641.91 [Kbytes/sec] received
Connnection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 1.9 0 13
Processing: 18 100 276.4 40 2739
Waiting: 1 97 276.9 39 2739
Total: 18 100 277.8 40 2750
Percentage of the requests served within a certain time (ms)
50% 40
66% 49
75% 59
80% 69
90% 146
95% 245
98% 449
99% 1915
100% 2750 (last request)