There are no changes, except to the upgrade price. If you paid for a full year of the perpetual licence under Studio One 7 Pro, you are entitled to all updates until 1 year after purchase. That includes the upgrade to Studio Pro 8. Your end-of-contract date remains the same. If you have a perpetual copy of V7 that has gone past that anniversary, you have to pay the $99 (£89) upgrade fee. Some early adopters have been lucky and received a 'free' upgrade even after their anniversary - or at least, they say they have. I'm waiting for some of them to realise they didn't cancel the annual payment! Some others have received a validity of 2 or even 3 years for their future updates, but the Terms are clear that it's a one-year contract.
If you have the Plus subscription, essentially it makes no difference to this process. If paid annually, you also have a perpetual licence, and the upgrade deal goes to the first anniversary of your last subscription payment. If you're on the monthly sub, you do not have a perpetual licence and you will not be able to keep any version of Studio One/Studio Pro obtained under that subscription should you stop paying.