This weapon will almost certainly be included in Fallout 4, as the name "Mean Green Monster" is a reference to the "green monster," which is part of Fenway Park, now known as Diamond City.
Someone may want to add this to the Fallout 4 weapons page, and add a link here. This is technically speculation, but it seems unlikely to be coincidental.
Speculation, unfortunately. However, you do have a point, and I also would not be surprised to see this weapon appear in Fallout 4. Thanks for the input, though - time will give us the answer when the game comes out in November. User:Sarkhan the Sojourner 20:41, August 19, 2015 (UTC)