To meet the increasing demands of high-throughput manufacturing, modern automation systems are increasingly being designed using a modular architecture, commonly referred to as modular automation. However, due to vendor lock-ins and high upfront investment requirements, the industry relies on existing legacy automation systems that were developed in a non-modular fashion. A major challenge lies in enabling the incremental modernization of legacy systems while ensuring their seamless coexistence with modular automation systems. To address this challenge, we propose a conceptual architecture for a containerized gateway that integrates legacy and modular automation systems. We present initial insights into the feasibility of using containers for such integration via a survey conducted with researchers and practitioners in the automation domain. Furthermore, we discuss an implementation plan for the proposed architecture in the automation industrial settings.