Yes April 2013 CU has been postponed and because of the issue in SP1 which has been pulled in.
The KB article for SP1 http://support.microsoft.com/kb/2850035/en-us has a link for the download SP1 which if you clicked now, gives you as below;
Lots of FAQ on Stefan Gobner blog http://blogs.technet.com/b/stefan_gossner/archive/2014/04/10/sharepoint-2013-sp1-and-april-cu-status.aspx a must read before you for any more updates.
Whenever Microsoft announces any other service packs or cumulative updates, you’d better wait, minimum 2 months if not more, during this time, check with forums, check with the Expert SharePointers all around, ask how is it going with the last update, wait till you hear everything is okay…
If you come and ask me, what if we are closing a project and whatsoever updates fixes a bug!! How would we wait?? .. I really have the same question but my answer may not be suitable for all cases.. I’d recommend to support the project as should be then install the update once you are sure it is ok.
I totally understand the pain this have caused for who installed SP1 L