They are just the old @MediaWikiMeet accounts renamed. I will start updating wiki pages referring to these accounts. If you still find a mention to @MediaWikiMeet please update it. Thank you!
Topic on Talk:Social media
@mediawiki accounts renamed
Please also update the central list at m:Microblogging handles and don't forget to use the !MediaWiki and !Wikimedia groups/tags.
Good idea, should I list @MediaWiki under "Official handles" or "Projects"? It sounds to me official but I rather check here before since I'm not familiar with that page and how it grew.
About using "!Wikimedia", is that string kept intact when replicating to Twitter? Just wondering about weird strings, and their effects on readers and search engines.
Yes, probably "official".
!Wikimedia is translated to #Wikimedia when forwarded to Twitter.