A gradual growth in flexible work over many decades has been suddenly and dramatically accelerated by the COVID-19 pandemic. The share of flexible work days in the United States is forecasted to grow from 4\% in 2018 to over 26\% by 2022. This rapid and unexpected shift in the nature of work will have a profound effect on the demand for, and supply of, urban transportation. Understanding how people make decisions around where and with whom to work will be critical for predicting future travel patterns and designing mobility systems to serve flexible commuters. To that end, this paper establishes a formal taxonomy for describing possible flexible work arrangements, the stakeholders involved and the relationships between them. An analytical framework is then developed for adapting existing transportation models to incorporate the unique dynamics of flexible work location choice. Several examples are provided to demonstrate how the new taxonomy and analytical framework can be applied across a broad set of scenarios. Finally, a critical research agenda is proposed to create both the empirical knowledge and methodological tools to prepare urban mobility for the future of work.