It seems the situation has evolved since end 2014 and now major RDFa implementations are 1.1. Recent documentation is for 1.1. As a trend indicator, a query on Google RDFA 1. gives only 1.1 results.
@daniel did you find RDFa 1.0 users? Should we make a call on the mediawiki-l mailing list?
@Dereckson I havn't investigated RDFa 1.0 vs 1.1 at all (hint: I'm not Daniel Friesen). I don't think I have looked into RDFa at all since I wrote the relevant code in Sanitizer some years ago, so I'm not very well suited to lead that discussion. Also, I'm trying to focus on T124792: RFC: Service Locator for MediaWiki core. Perhaps ping @DanielFriesen
So, all the current documentation and publications are about 1.1
Noone answered the public call made per Tim suggestion to get input from external users at https://lists.wikimedia.org/pipermail/mediawiki-l/2016-March/thread.html, so it seems it's safe to go on in the process.
The RFC contains rationale, methodology, a code (to rebase) and now a lack of interest of stakeholders to keep RDFa 1.0. As such, it seems ready for discussion for me and it could be interesting to discuss it in next RFC office hour.