I'm glad you like the project and this is a great suggestion.
It wont be as much work as you think it is to implement because I had made plans to add AO and Emissive outputs and previews support from a while back. Custom outputs too. It's a bit too late to add them to the upcoming release as it will be out in a few days so i'll have to add it to the one after.
Keep the suggestions coming. If you make some cool stuff, post it here https://itch.io/t/611017/post-your-textures