Count me as one who is thankful that SketchUp doesn’t include a rendering engine!
One of the things that continues to impress me about SketchUp is that, for the most part, they’ve striven to keep to the basics, which for SketchUp is to be an incredibly powerful surface modeler. At the same time, they allow extensibility through plugins/extensions.
In programming terms, reading this forum has led me to understand that rendering is very different from modeling. Thus, adding rendering to SketchUp would represent both significant investment and, more importantly, a tangent away from their core expertise.
I think Trimble (the makers of SketchUp) is wise to leave rendering to others. Partial evidence of this is the wide range of plugins/extensions available through Sketchucation and the 3D Warehouse.
As a person trained (long ago) as a programmer, it boggles my mind to consider the software bloat that would be involved if Trimble tried to implement even 10% of the available extensions/plugins as native tools!