I noticed this yesterday afternoon 27/12 and I too have a vested interest in the BA 208 for mid May and I was emailing a friend who is in a similar situation who contacted BA and were told that the flight will be cancelled. No sign yet that this is happening but I do believe the zeroing out of all fare buckets is normally a good indication that this will happen especially as the other flights that day are scheduled to be operated by an A380 (so far). My set of flights have already been changed once due to the LHR-MCO flight being discontinued and I used the opportunity to change both airport and dates to suit. Now it looks as though another change will be highly likely.

Oddly EF shows that the AA codeshare information shows the flight is operated by a 789 not a 781.