The story for opensource game development is almost complete. All the requisite programming languages are available and there is a legitimate tool chain for digital content (Blender).
Game engines already target linux (UE & GODOT), although perhaps not as first class citizens.
The one refrain I always here is the need for more sophisiticated debugging tools. This is the one saving grace of Visual Studio.
Could Canonical invest some funds and lend some engineering support to x64dbg to bring the debugger to linux, or, if closed source solutions are not off the table, the RemedyBG project.?