Design innovation that accommodates customers’ affective needs along with their cognitive decisions suggests itself to be of primary importance for a system to convey more added-value. Product development should accommodate complicated interactions among human users and multiple products, and thus entails the need for systematic modeling of users’ affective states in conjunction with the cognitive process. This paper adopts a perspective of designing product ecosystems with a particular focus on the activity-based user experience (UX). To model the affective-cognitive aspects of UX, a modular colored fuzzy Petri net (MCFPN) model is developed to capture the causal relations embedded in users’ affective responses and cognitive processes. The method is applied to design a product ecosystem of a subway station. Initial findings from simulation indicate that the ecosystem perspective of product design is a useful step toward affective-cognitive engineering, and the MCFPN formalism excels in incorporating UX into product development.