There has been no fixed date for version 5, neither in this or other topics loosely mentioning version 5. There is also no certainty/indication that it would go through 4.9 before 5.0, again not something I worry about, I will take what updates there are as they become available.
In previous topics it has been suggested that version 5 will require a clean install, I don't know for sure if that is the case and isn't something I will worry about I will just do it if that is what is required. I'm sure we will get notified if that is the case.