ProBoards has not announced a Launch Date for v6 and I reckon that won't happen for several months. Once available, we'll have the option to enable it (or not) on selected themes. The use of v5 (what you see now) and v6 will be concurrent for 18 months. After that, v6 will be mandatory.
Anyone who would like to experience the look and feel of it can go to the ProBoards Support Forum and create an account there. Follow the instructions in the ProBoards v6: Support Forum Alpha 2 thread to configure your Support Board account so you can navigate that forum using v6. It's still in raw form and has a substantial number of bugs but you can get some familiarity with it.
Feel free to discuss any matters related to v6 here, although there is a board Alpha 2 Feedback where you can post your own thread providing feedback and get a reply from one of the ProBoards Development team.