There was a discussion in April on the mailing list about having a deprecation policy based on the one for the MediaWiki interface. Did this go anywhere?
I am asking because I have been bitten by a breaking change - specifically, this removal of APISite.getuserinfo() broke my bot on Toolforge. I am not saying the removal was unreasonable (2+ month after the "deprecated" decorator was added sounds reasonable) but there is no documentation of expectations anywhere I could find.
(My bot breaking is 95% my fault, since I did not notice the breakage in timely fashion, nor did I regularly review the Pywikibot code for deprecation tags, so even a one-year deprecation period would not have helped me much, but still.)