I think an engagement announcement right now would be horrible timing. The Queen and Philip have made it so far, they should have at least one moment that is all about them, and likewise, a REAL engagement announcement should be special for the couple involved, and as the Wedding Anniversary is already there, at the same time each year it should have precedence, since they aren't going to go back in time and say, hey, lets get married a couple months from now so that our future grandson and his future fiancee can announce their engagement before our 60th wedding anniversary........... An announcement can be made anytime, and if they truly love each other, it shouldn't matter how long they have to wait. Younger generations need to learn patience. Sure, they could tell the Queen and Philip that they want to get married, and they would probably be delighted, but leave the public out of it for now.