I don't think modelr is going to change significantly in the future. It solved a pressing problem (fitting models as part of a pipeline) so I could teach modelling using the same interface as everything else in the book.
However, the modelling infrastructure in R is generally showing it's age, and thinking about how to make modelling easier is something that I will be working on in the coming months.
I saw the vctrs package repo the other day on your GitHub. What's your plan with that? I guess your covering all of R's base data types (dplyr:data frames, purrr:lists, forcats:factors, vctrs:vectors)? Also do you plan on developing further functional programming packages?
However, the modelling infrastructure in R is generally showing it's age, and thinking about how to make modelling easier is something that I will be working on in the coming months.