The only way to enjoy maximum flexibility and freedom on the AC100 will be to install an open operating system. Obviously the most common choice will be a Linux flavour. Some may also want to have a DualBoot option as well, with the Original OS as fallback.
From what we read in various blog postings, Ubuntu, Debian and ChromeOS are the most promising candidates. The Gentoo page has instructions for installing Gentoo and contains hints for porting other distributions.