Edit: Thanks to the commenters who checked the Membership Rewards site ad found that the ability to transfer between MR and Avios has returned at a 1:1 transfer ratio.

Just now at 10:40 AM Paris time, 4:40 AM ET, and 1:40 AM PT, I logged into Membership Rewards to see if the 50% transfer bonus between Membership Rewards and Avios had really ended.