So many possibilities...
I have two other primary hobbies: music and brewing beer. So I'd probably either have a sweet recording studio in the room that's my main game room, or an ultra-elaborate homebrew setup.
I also like cars. I currently have a nice '65 Mustang convertible in the garage, but have on more than one occasion, considered selling most of my arcade/pin collection in order to pick up a Delorean for myself or a '59 Impala for my dad.