Hello,
We agree with your request and have recently been discussing having parametric models in the 3D View for accurately previewing non-square textures and materials.
In the meantime, please note you can use the graph's Physical Size property in combination with the shader's 'UV Scale Enabled' property to scale the UVs to match the texture's ratio, as shown below:
I hope this helps, and thank you for your patience!
Best regards.