Yes, as I pointed out in my question, I am well aware of the fact that CF11 only supports Ubuntu 13.04 and 13.10 non-enterprise grade and no longer supported by Ubuntu OS. However, 14.04 is not very different from 13.10, and the issue is how the CF11 installer handles Ubuntu's deployment of fairly stock Apache 2.4.7.
Regardless, I figured out the problem - the installer does not like the existence of an httpd.conf file in /etc/apache2. So, it installs and works once I removed the errant httpd.conf file created by an aborted CF9 install, other than some customization we have done for our old CF9 installation. However, the CF11 installer is still very poorly designed as it does not adhere to how Apache 2.4.X (or 2.2.X) and Ubuntu have laid things out. The installer should really place a config file in /etc/apache2/conf-available and create a symlink to it in /etc/apache2/conf-enabled.