Updated Ranking

Engine Code Viability Conceptual Fit What to Steal
Wargame Engine Alive (2024) Node-tree matches graph Rendering code, GUI, scene system
Fabula Dead (2012) Client-server matches exactly Architecture pattern, event protocol design
Sequtus Dead (2012) Low RTS patterns (selection, orders)
OpenRTS Dead (2006) Low Isometric tile concepts
Godot Alive Wrong runtime (GDScript, not Python)
Panda3D Alive Wrong domain (3D)
OpenRA Alive (C#) Wrong runtime, design patterns borrowable Trait system mental model, map format concepts