New Graduate + Learning Swift and iOS development

I am currently a new graduate working at a financial institution as a new grad developer. We use mostly Java, SQL, and pure JavaScript on the front-end. I am required to have 2 rotations in a year where I can choose teams to work at.

My current team works on trading algorithms and our trading engine. However, I have opportunities to explore other areas such as: data science and machine learning, iOS development, data analytics and low-latency trading (C++).

I personally am learning towards either data science or mobile development (we only have iOS). However, I find that Swift is highly specialized language, mostly useful if one goes to become Apple products developer. In the meantime, data scientist position would require to learn more on maths and stats on the job + programming in Python, R and Java. The latter sounds as a more difficult skill to achieve on my own while iOS development has plenty of resources to learn more about.

From the market perspective, as well as not being into specializing, I was thinking that working with Java in current team and then doing data science in another would provide wider employment opportunities than specializing early in something niche like iOS. What do you guys suggest?