It is not clear from the documentation what the intended usage is for outputs from stan_lm or stan_lm where you do not have hierarchies to pass to gather_draws() or spread_draws().

For example, fitting a very simple model with stan_lm():

library(tidyverse)
library(rstan)
library(rstanarm)
library(tidybayes)

test_stanlm <- stan_lm(mpg ~ cyl + disp + hp + drat + wt + vs +

Although you clarify in readme that run_model() "takes a long time", the status message could use some more information. The first message I see for at least a few minutes after running this function is:

Processing function input....... 
Done. 

... and although the function is still processing, I see the word "Done" for some time.

I suggest improving the information in the me