The memo reads:
Starting March 30, iPad 4th generation whole unit repairs may be substituted to iPad Air 2 models. Apple's repair and order management tool will indicate for each repair if a substitution will take place. Please note the substitute part’s color and capacity to ensure the customer understands what their replacement iPad whole unit will be.
The decision to replace rather than repair will be decided on a case-by-case basis and is likely dependant on availability.