Animaniacs Vol. 4 has yet to be announced, so there is no proper answer to your question.
With Blu-Ray soon be a replacement for DVDs, Vol 4. could never see the light of day on DVD, and it is very doubtful Warner Bros. would continue the series on Blu-Ray in such a incoherent release on the new format. Warner Bro. would probably start over from vol. 1.
The best thing you can do is gather as many fans of the show that you can and have them, as well, as yourself to request Warner Bros. a release via e-mail. From there, you can only hope.
Yes, it was released in February 2013.
Animaniacs - 1993 Hooked on a Ceiling Goodfeathers The Beginning 1-4 was released on: USA: 16 September 1993
Animaniacs - 1993 Papers for Pappa Amazing Gladiators Pinky and the Ralph 4-6 was released on: USA: 19 October 1996
Animaniacs - 1993 From Burbank with Love Anchors A-Warners When You're Traveling from Nantucket 4-5 was released on: USA: 28 September 1996
Animaniacs - 1993 A Very Very Very Very Special Show Night of the Living Buttons Soda Jerk 4-4 was released on: USA: 21 September 1996
Animaniacs - 1993 Ten Short Films About Wakko Warner No Time for Love The Boo Network 4-7 was released on: USA: 2 November 1996
Animaniacs - 1993 De-Zanitized The Monkey Song Nighty-Night Toon 1-1 was released on: Japan: 13 September 1993 USA: 13 September 1993 Brazil: 4 April 1994
as of 2010, warner brothers has confirmed "no plans at this time"
there is no .hack GU vol 4 it only goes up to vol 3
Drunk History - 2007 Drunk History Vol- 3 Featuring Danny McBride 1-4 was released on: USA: 2007
Drunk History - 2007 Drunk History Vol- 4 Featuring Paul Schneider 1-5 was released on: USA: 2008
The cast of Real Couples Vol. 4 - 2001 includes: Bonlie D