I mean i never would have signed up to develop an R-package on my own. But I was at the right place at the right time to work on a project with funding that is interesting and it just happens to be in R. It's nice to learn a new tool (no matter what it is), but I would not have chosen R if it was my choice.
Moreover, I think sometimes people get their PhD and think they deserve to use the tools they put in their toolbox, on the problems they focused on, and don't see that all they really did was get a ticket to the game. Most scientists have a phd. Most scientists don't work on the thing their PhD is about ten years later. The sooner you open up to that the sooner you will get out of the postdoc chase and get a job that is a lot more rewarding (both intellectually and financially). All this means that there may be problems you are going to learn about and focus on that you never thought you would at some point, and being open to that and seeing it as an opportunity will carry you further then not.
Moreover, I think sometimes people get their PhD and think they deserve to use the tools they put in their toolbox, on the problems they focused on, and don't see that all they really did was get a ticket to the game. Most scientists have a phd. Most scientists don't work on the thing their PhD is about ten years later. The sooner you open up to that the sooner you will get out of the postdoc chase and get a job that is a lot more rewarding (both intellectually and financially). All this means that there may be problems you are going to learn about and focus on that you never thought you would at some point, and being open to that and seeing it as an opportunity will carry you further then not.