OMG! They have made it! To be released in January.
Only one question remains: will Ecto-1 fit inside?
From Lego's facebook page:
$399 CAD, 4600 pieces. Full interior.
9 Minifigs: Peter Venkman, Raymond Stantz, Egon Spengler, Winston Zeddemore, Janine Melnitz, Dana Barrett, Louis Tully, Zombie Driver and Library Ghost. Also comes with Slimer, Pink Ghost and Blue Ghost.