Within urban mobility ecosystem, Mobility-as-a-Service (MaaS) has come up as a promising approach to promote sustainable modes of transport and increase the attractiveness of public and shared multimodal mobility. It aims to become a viable alternative to personal cars for door-to-door trips. The long-term objective of MaaS is to change the people's travel behaviour by nudging them to make sustainable choices. However, changing people's travel behaviour is not easy and MaaS has to provide personalised mobility services, catering to the needs of each individual user, in order to be considered as convenient as a personal car. In this paper, we look at the existing literature on personalisation in MaaS proposed by the research community as well as different private MaaS service providers. This brief literature review helps in better understanding the current trends on personalisation and highlights certain limitations in the way it is incorporated within existing MaaS solutions. Based on these limitations, we discuss certain challenges which need to be resolved in order to improve MaaS in the future. These challenges present interesting research directions towards the development of personalised sustainable urban mobility ecosystem.