I like the JetBrains IDEs, but the Rust support will likely become a paid feature in the future. Go support was free while it was being developed, but the Go plugin is now only for the Ultimate Edition.
It's MIT licensed. It's not clear to me that it's developed by jetbrains at all, but if it is, there will probably always be an open source version, if only because it gets forked.
I believe there is some ‘official’ support for that plugin, I vaguely remember reading that JetBrains was devoting a small amount of resources to aid in its development. Though I can’t imagine it would effect the license
The author of the plugin works at JetBrains and works on it on his day job.
The plugin already has paid features in the sense that the debugging support only works in CLion. That seems like a likely future path to me.