It is finally happening, collaborative coding in IntelliJ! And it's not even restricted to IntelliJ Ultimate (for now).
All you need is an IntelliJ 2020.2.x build and an internet connection. Just install the plugin and share a collaboration link.
The other side then has to quickly install a dedicated IntelliJ Client and you're good to go.
From what I've seen during a quick test run it looks pretty stable and promising. And I'm not sure if I'm interpreting the connection UI correctly...but it seemed that the connection was peer-to-peer, with JetBrain's servers only used for lobby management. That would be a huge plus if true!