Having watched the warning about default priors not remaining the same in future versions of rstanarm for the umpteenth time, it occurred to me that there was a kind of tension between the aims of rstanarm to provide a sane set of defaults for a broader set of users, and the need for reproducible research.
Inevitably many people are going to use the default priors because i) it’s easy and ii) they are sensible and seem to reflect your thinking on good guidance in the absence of an informative prior. However if you do change things in future then it would make it hard to reproduce an older analysis.
I wondered if it would be possible to store the values for priors in each new release, and then allow users to specify a date to pin the priors to? That way it would be possible to recreate an older analysis by simply typing lmer_stan(…, pin=‘1 Jan 2017’).