I tried flashing on the fly in my Zgemma H9 Combo with a new 6.5 of 2nd May but at the end it was not visible at all.
So, my conclusion - from what Delfi has told us - is that if you flash a new image and succeed, all other images might be lost. Incompatibility is the key word. Maybe in a week or two one might have compatibility again and in that case the most likely outcome will be - new flashing of everything from scratch... Maybe it's better to be patient and wait for this one to blow over...???