I see a security concern in introducing a new file extension.
It's common to configure a web server to pass locations that end with .php
to a PHP interpreter.
Nginx example:
```
location ~ \.php$ {
include snippets/fastcgi-php.conf;
fastcgi_pass unix:/run/php/php8.2-fpm.sock;
}
```
Apache2 example:
```
<FilesMatch \.php$>
SetHandler application/x-httpd-php
</FilesMatch>
```
With a new file extension, users would be forced to change their configs,
or a direct request to .phpX file would expose its source code.
This will come as a surprise to users who don't know about the pure syntax
yet include libraries that use it.
