It should be possible to query a user's contributions by their user ID. IDs are more robust identifiers than usernames since usernames can be changed. Currently, there's no way to look up a user or filter results by a user's ID number.

For example:

• list=usercontribs allows for ucusers -- should have something like ucuserids
• prop=revisions allows for rvuser and rvexcludeuser -- should have something like rvuserid and rvexcludeuserid
• list=users allows for ususers -- should have something like ususerids
• meta=globaluserinfo allows for guiuser -- should have something like guiuserid that takes a global user ID