Good news! Today, on January 16th 2018, Oxford University Press (OUP) announced its participation in the Initiative for Open Citations, and requested Crossref to turn on reference sharing for all OUP deposited references from more than half a million publications. Oxford University Press is the largest university press in the world, publishing in 70 languages and 190 countries.
Their announcement is at https://academic.oup.com/journals/pages/announcements_from_oup/oup_joins_I4OC.
OUP now joins the elite band of four university presses that have already made their references open at Crossref in response to the I4OC call (https://i4oc.org/#publishers).
This decision by OUP has been a long time in gestation – see my 2012 post Oxford University Press to support Open Citations – but is no less welcome for that!