In his latest .plan, Todd Hollenshead, from id software, shared his experience with GBA DOOM:
Also, a quick brag that while I was on trip week before last, Adrian Carmack and I
managed to play the first GBA DOOM deathmatch at DFW Airport and also on the plane
with what was a final build of the game (which is now off to manufacturing).
I think the flight attendants were a bit aggravated by the link cable being run across the isle but it was tons 'o fun.
This clearly means GBA DOOM will be released shortly. Thanks go to Wilf for having pointed this out.