The plan for the Aquatic update is to have it out first for the Java Edition, Xbox One, Switch, mobile, and Windows 10 versions. The PlayStation 4 and the aforementioned prior generation of consoles will get it a bit later. It's not very clear as to why the PS4 version is getting it later, but it is what it is.
With the exception of PlayStation 4 Edition, this will mark the last big effort to keep those editions up to date with our newer versions of the game. Although we’d love to keep bringing new content to all our players forever, the older generation of consoles now make up less than 5% of our active players, so we’ve made the difficult decision to focus our efforts to support players where they play Minecraft the most and where we plan to add new features: on Java, PlayStation 4 Edition and the versions of Minecraft made with the Bedrock Engine on other consoles, mobile, and Windows 10.
Mojang also notes that the older versions of Minecraft that are still playable on the Xbox One and Switch will not receive the Aquatic update at all. This is because players on those versions can already upgrade to the current version of the game for free.