This is a continuation of the github issue at https://github.com/IATI/IATI-Schemas/issues/30
Currently both iati-activities and iati-activity have a version attribute, which serve the same purpose (of identifying the version of the standard used).
The majority of publishers currently use iati-activities/@version only. No publishers use iati-activity/@version only.
iati-activities/@version is easier to work with, because it is one single place to check to see what version of the schema a file should validate against. With iati-activity/@version it is possible that multiple activities in the same file would specify multiple conflicting versions of the schema.
There is a similar situation for iati-organisations/@version and iati-organisation/@version.
Since removing an attribute would break backwards compatibility, that would only be suitable for an integer release. However, in the short term it could be deprecated.