The release notes for MySQL 5.7 DMR5 are starting to take shape on dev.mysql.com.
For me, what is one of the most exciting changes is that “Strict SQL mode is now enabled by default for transactional storage engines”. This aligns very nicely with a post I wrote just recently about transitioning changes using initially a whitelist and then a blacklist.
User’s with legacy applications still be able to opt-out of STRICT mode, but importantly new applications won’t be accidentally trapped into sub-optimal defaults.