Here is list of issues that need to be fixed before 0.13 release. I only list breaking changes and omit things that could be added to 0.13.1, etc.

• Split streams into separate package Separate streams into a separate package #355
• Decide what is best way to expose constructors for vectors. It have been requested numerous times: Export data constructor for boxed vector #245, Nowhere seems to export the constructor to Storable vector #343, Feature Request: Make underlying representations accessible #171, add Vector (a,b) -> (Vector a, Vector b) et al to Unboxed Vector and MVector #63 (tangentially related), Vector.Unboxed doesn't export constructors, but Unboxed.Mutable does #49. It's of course totally unsafe. Still it's very useful to have on occasion
• Determine semantics of slice/grow/etc semantics of slice, now and future (plus near term bug fixes) #276, Semantics of grow/unsafeGrow #36. Likely it's going to be a documentation change but it's better to do this for 0.13 just in case.
• unfoldrN, unfoldrNM and fromListN are dangerous unfoldrN, unfoldrNM and fromListN are dangerous #301. Could require change to semantics of functions.
• The Bundle datatype seemingly doesn't need the field sVector The Bundle datatype seemingly doesn't need the field sVector #269. Not terribly important but certainly breaking
• decide semantics of maximumBy & friends