Free space optical communication (FSO) systems have recently regained great interest as a potential wireless interconnecting solution for 6G era, thanks to their ability to meet the main requirements of high capacity, low latency, energy efficiency, dense connectivity, and high level of security against interception. In this article, we first review the main challenges and opportunities that FSO systems present toward the deployment within 6G networks. Furthermore, we propose a modular FSO transceiver concept for a reliable, cost-effective, and high-capacity FSO system. The design principle consists of subdividing the FSO transceiver into modules, which can be independently developed, replaced, upgraded, and easily integrated within other systems. Successful integration of each module facilitates the customization to meet the specifications of different applications while considering the preferences of the customers. We also introduce our newly developed modular FSO transceiver and discuss its long-term performance for fixed and mobile platforms. The obtained results demonstrate that the proposed concept has significant potential in advancing FSO technology toward its adoption in 6G era.