Some of the big items:
* Deprecation process: what should the "suitable timeframe" be?
* Remove obsolete output formats: removing txt, yaml, and a few others
* JSON output as default
* Changes to JSON output format, e.g., UTF-8 default, true instead of empty string for boolean
* Removing links in pretty-printed HTML formats
* Removing "possible errors" & "props" from action=paraminfo
* HTMLizing & localizing action=help (please speak up if you're using action=help from a client)
* A complete and utter overhaul of token handling
* Removing long-deprecated parameters, e.g., "title", "watch", & others
* Deprecating prop=imageinfo, rewriting from scratch as prop=fileinfo