I'm afraid you will get what you see - new UI with responsive layout with less or same functionality. PHP 7 + new libraries are already implemented in 6.2 branch so for brain free user the big change will be new UI. Developers obtain new REST API.
Group Office lost many users because there weren't big changes for 3-4 years? People simply moved to different platform which already includes responsive or mobile application and hundreds modules so you can simply set up your business. In short big changes (for users) were in 4.x branch. 5.x brings just new UI and 3rd party libraries and 6.x replaced project module and nearly implemented new license model where you pay for the module not whole Group Office. It could open the door to other developers because all modules could be at one place but 6.1 return back to old license model. Of course there were a lot of bug fixes and minor improvements but except holidays module nothing big for end users.
That is pity but that is true. I know companies who simply changed CRM because GO stopped in time. Why should you pay for support when 4.x branch was more stable and had similar functionality like 5.x or 6.x? Why change projects module when old one was suitable for you and you have no option to stay with old. Changes are needed however your should have always option to choose. For many users is CRM bad word and when you change the flow or UI? They will try kill you
Anyway we can only hope for the future
My information about new UI are 7 months old so maybe there will be something special for us.
IT Analyst, Independent seasoned Group-Office developer, Educator of web applications