The other problem with this idea is that I don't believe that the source code for the UniFi controller is available, and Ubiquiti (as far as I know) has not built binary packages that are compiled for either MIPS (RB4xx/7xx) or PPC (RB800/1xxx). Even if you got Debian core + APT all running inside of MetaROUTER, the UniFi stuff is not going to install and run inside of it because they have only made packages for x86/x64.
So you would need Ubiquiti's cooperation to make this work.
EDIT: Well it looks like I should have done my homework first before spouting off. Many components of UniFi Controller are open-source (not written by Ubiquiti; e.g., MongoDB), and those that are proprietary are actually written in Java. So although Ubiquiti does not provide DEB packages for hardware platforms other than x86 and x64, you can build all of the components for your preferred hardware platform by hand (including a Java runtime) and get the software to run on non-Intel hardware platforms that way. See: http://community.ubnt.com/t5/UniFi/Unif ... d-p/299859