It's done 5.3 finally, after quite some discussions, reached beta state. So if you're not already on it it's now the perfect time to test it. Problems found now can be fixed before we mark it stable. Issues not find might need workarounds in your software which will cost you more time in the end. Or the way I often put it: Test now and complain or don't test and live with the consequences - we do our best but we certainly can't cover every edge cases especially in a version like 5.3 where we did quite some internal cleanup and added tons of new features.
The NEWS entry file is, compared to some previous alpha versions, quite short this time but still worth reading if you tested a previous alpha release.