According to a post in the 5.3 thread (roughly 2 weeks ago) - 5.4 was released "to new trials" . I don't believe they will post Release Notes till it is released for everyone including self hosted sites.
This was the longest period in between updates since we have been using test rail. The same post said that there is going to be an additional release after 5.4 for more features.
Looks like 5.4 mainly adds Win Server 2016 and PHP7 support, then the additional release will do more straight features.