The learning curve will come with DAX and model building.
Power BI is a really exciting product. It's fast paced, the Community is growing and really interactive, there are a bunch of ways to learn and interact (Power BI User Groups).
The major benefit I see is that it's an avenue to take the data that you've already been working with and helping business make that data useful. Power BI is a tool that makes that really straightforward, especially if you come from the MSFT technology stack of experiance.
In many ways, it is an extension of your skill set, and knowing it will definetely help in the future when SSRS and Power BI work together more closely.