This seems like a bug to me. The docs for ?import_list say the return value should be a list, "If rbind=FALSE (the default), a list of a data frames. "

Here is a smol reprex.

list_obj <- split(iris, iris$Species)

str(list_obj, 1)
#> List of 3
#>  $ setosa    :'data.frame':  50 obs. of  5 variables:
#>  $ versicolor:'data.frame':  50 obs. of  5 variables:
#>  $ virginica :'data.frame':  50 obs. of  5 variables:

jsonlite::write_json(list_obj,"tst.json")

str(rio::import_list("tst.json"), 1)
#> List of 1
#>  $ :'data.frame':    5 obs. of  3 variables:

str(jsonlite::read_json("tst.json"), 1)
#> List of 3
#>  $ setosa    :List of 50
#>  $ versicolor:List of 50
#>  $ virginica :List of 50

^{Created on 2019-02-03 by the reprex package (v0.2.1)}

In building this out I found that rio::export(list_obj, "tst2.json") raises an error and think that may be related. The docs for export say "An exception to this is that x can be a list of data frames if the output file format is an Excel .xlsx workbook, .Rdata file, or HTML file. See examples.)" and my feeling is that JSON files should be included in these exceptions.