Our license issues have been sorted out and I've been able to test the idlw-shell capabilities of the emacs-upstream-merge branch. I had to make a few small tweaks to the help system, as often happens with new IDL releases, but the (funky old) completion and other features continue to work pretty well. I merged the branch to master and mentioned ELPA in the README.
One question I had is what happens to the texinfo manual for ELPA packages, and if they need any special treatment to get installed. I am also not 100% sure this will load correctly as a package given the file re-org I did some time back; I've been testing it using a use-package :load-path and that works, but nothing like a real test of the live package. Can always give it a try after it lands on ELPA and make any changes needed.
Other than that, and any pending suggestions or concerns you had, I think I'm ready to flip the ELPA switch.
Thanks for your work on this.