The critique against Nexus Q has been unison. It has to few ways of playing music for its price tag. And even if it where half the price, who would want a audio player that only can play content from Googles online services? There are such things as mp3s, music services like Spotify and Internet radio out there that many would consider a base requirement for what the Nexus Q should be able to play.
Google has drawn the right conclusions from the critique and halts the product launch in order to add more features before it will launch again. No new release date has been presented and it will probably take a while to implement new features that will please the crowd.
Possible new features:
Ability to play different audio files (like mp3) from the local network.
Ability to transfer audio files to the device storage.
Support for Internet Radio.
Support for more online services. Hopefully Spotify.
Upgraded OS version to Jelly Bean. Because it will take a while before relaunch, an upgrade is necessary to avoid negative critique for an outdated OS version.
Ability to play a few video formats from the local network.
Everyone that has pre ordered Nexus Q from Google Play will get it for free, which is a nice gesture from Google to the brave few that has planned to fork up 299$ for it.
It should be pretty clear to Google what people want from the device by now so it is up to Google whether they want to be a serious contender for the multi-room audio (and video) throne or not.