Working on a research topic, I am faced with this question " How can we propose a Product Portfolio Management framework for Engineer-to-Order industries?" Although, these industries have certain product families, they offer totally different products to their customers, based on what customers need. Sometimes they accept orders from customers, they design products and services just for them, but at the end they notice that the process was not as profitable as what they expected.
So, how can these industries define their product portfolio in a way in which they still have demands and the whole design, manufacturing and delivery process remains profitable for them?
Are there any related case-studies or articles in the literature? Thank you for your help and kind answers in advance.