Devtools is generally stable, most of the active development has moved to sub-packages like remotes and usethis, and relatively little code lives in devtools itself.
I don't know of any major outstanding issues in devtools itself.
The package development cheatsheet likely needs a major overhaul to account for much more functionality in usethis and the current state of devtools. r-lib/devtools#2107
Should devtools be converted to use pak for installation, or should the installation commands be deprecated in devtools and users suggested to use pak directly?