The wording you’ve used feels a bit “janky,” but to answer the best I can anyways:
You could use C++ to make mods, or Visual Blueprint Scripting.
I’m unsure of what you mean by this. Do you mean if there will be modding tools that assist in modding? Do you mean to ask if something like a plugin repository with core framework will exist again? Do you mean to ask if mods are still supported?
The answers are “yes,” “RocketMod is not an official tool and is community-made just like every other plugin repository and framework for Unturned 3,” and “yes.”
The “etc.” would have been useful, but this is technically already possible in Unturned 3. Although undocumented, you can change Unturned 3’s UI and there are client-side mods and such (although in Unturned 3 this is really just a localization thing).