Couldn't find an official statement, that the Unity3D development software will run under Linux.
It sounds more like the new update will only allow to build _games_ that run under Linux [1].
You aren't, or at least they haven't published any information about it yet.
On their website they state "Publish to Linux", not "develop on linux", and their "introducing Unity 4" video[1] show Os X compiling for Linux.
I hope to be wrong too, but anyway it's still better than nothing.
You are not wrong. We will not be shipping the Editor for Linux, only export options for players that will run on 32-bit (x86) and 64-bit (amd64) Linux. We are only going to offer official support for Ubuntu Linux with vendor-made graphics drivers, but we expect games exported from Unity will run on most modern Linux systems.
Still... VERY interesting possibilities open up if a game server can be run on Linux. Cloud based Windows licenses KILL the pocketbook once your users grow.
So even if it is not the Unity IDE... it's still good news.
Game servers for Unity can already be run on Linux. You'd write a multiplayer game in such a way that it just uses vanilla C#, and data structures that are easy to replicate (like Vector3, Transform, etc).
Running Unity apps themselves on the server even with this announcement would be a big mistake, IMO. It is not a stable piece of software.
I hope I'm wrong.