OP was asking if Rocket was required to run plugins—they didn't necessarily ask about the popular Rocket plugins themselves. Rocket is/was just a framework people preferred to use to make plugins, although it's not needed to make plugins in U3.
The same applies to U4, in which you shouldn't need to use a third-party framework to be able to run plugins on your server (similar to how you don't need a third-party tool to be able to run the game with mods). But it will also be much easier to mod the game, including in ways that would essentially just be various U3 plugins.
As far as your question goes (having features that resemble popular U3 plugins), there's features and tools we want to implement that make server hosting a better experience, but we aren't specifically targeting popular plugins to add them as official features.