I looked everywhere and found nothing about it. I also tried contacting sales, but it seems to not be working. So, to the forums:
I will release a professional project on the 20th this month, and I need to get Pro to remove the splash screen (I have to, case closed). But the new plans are not live yet, and the old ones are very expensive, and come with a 12 month commitment.
So, if I subscribe today to Pro with Android and iOS Pro ($225/month), once the new plans come out, can I switch to it without breaking the subscription contract? I know UT is calling owners and subscribers to make an offer, but I’m not one yet.
Nobody? Not even Unity people?
Why isn’t it like the past, where we could buy 3.x and get 4.x when 4 was announced?
The idea of the subscription is you always get the new version as it is announced. It will still be on Unity 5.x with the new subscription. I would hope they could fast track you onto the new subscription. The lack of reply could be down to you have asking on a Saturday, which isn’t normally a working day, plus many of the staff will have been busy this week at the Unite conference.
I can understand Unity making big announcements at their own conferences, and those conferences require lots of their staff, but they do need to be able to deal with people such as yourself who are affected by their actions in cases that require urgent responses.
Yeah, probably better to wait until next week to ask them.
The thing about the version is just the policy, why will anyone subscribe to the old plan when the new one was announced? All new subscribers should be automatically able to switch to the new plan, not even needing to go through a sales person.
Hello monday! 
Unity folks, do you know the answer to this? Can I subscribe to the current model, certain that I can migrate to the new one? Also, can I subscribe to Pro today, and then migrate to Plus? All that without breaking the 12-month contract?