Transition issues are always tricky. They will bear watching. JetBlue's loyalty staff has always impressed me as the brainiest of all airlines. I expect that they have thought of everything, including pre-qualifying customers who have met the eligibility requirements retrospectively.
I hope so. I was fairly disappointed with the change to the January start date, as I lost a decent number of potential point due to the transition.
My questions are these now: How long status lasts and how frequently you get the six EMS seats?
I am also concerned about the priority boarding. Now you have about 30% of the plane boarding first with the EMS seats. What percent are going to be boarding as "Mosaic" members combined with EMS seats, 50%, 60%? This quickly turns the priority boarding into a zoo scene, as has already happened on most of legacy airlines, where everyone is considered "priority" now. If everyone is priority, then no one is really priority.
JetBlue boarding right now relatively is calm and stress free, which I hope does not change...