The increasing demand for high-speed low-latency connectivity and ubiquitous coverage from various applications and services drives the evolution of communication technologies. At the same time, aviation passengers expect to consume services such as web browsing, audio and video streaming on the move, and to stay connected while they are on board an aircraft. Adding in-flight connectivity is a huge investment for the airlines, and the business case analysis to determine the return of investment is complicated. In addition, forecasting passenger demands is complex, especially with the evolving landscape of connectivity and entertainment. On-board Wi-Fi may soon become overloaded in the course of future connectivity requirements and regulatory restrictions. Thus, the advancement of 5G/6G technology presents an opportunity to revolutionize the in-flight passenger experience and generate new revenue streams for airlines. This study investigates potential use cases for in-flight connectivity and prioritizes them based on a set of criteria. Selected use cases are modelled in detail and the revenue calculations are presented assuming a typical operational year between 2035 and 2040. We further elaborate on the price assumptions and the methodology used to summarize the information from the interviews we conducted with a diverse range of parties. At the end, we develop a roadmap that comprises five steps to establish in-flight connectivity