It looks like, you need to get your Dolphin site up to speed on 7.4.2 and then 'maybe' moving over 'might not be a problem'.
Unless Deano wants to 'grandfather in' Dolphin users, you will also have to pay a 'monthly' licensing fee.
Deano is active now, and hopefully he will keep up with the project.
For now, I would say: Make sure any 3rd party modules you have work on a Dolphin 7.4.2 install.
Then sit tight for a while