My main issue, one that is especially relevant to gaming, is with the shitstorm around Mir. I would be thrilled if Valve built off Debian, however I would be disappointed if their interpretation of 'open' was strictly literal (GPL etc) and did not take in to account the fact that cooperative and collaborative interactions with the larger linux community are equally (if not more) important. SteamOS is also not the only distro that valve is targeting, so going down a road that reduces support for other distros seems like a rather stupid idea to me (and yes, I am saying that Canonoical's current behavior is isolating their platform from other distros).