Um, There's A New, Official Quake 1 Episode Out
Machine Games' DOPA
Depending on to what extent you accept 'Bethesda' as official, of course. This isn't id's work, and it's definitely not Quake-era id's work, but it is the work of neo-id's stablemates Machine Games - they of the improbably good Wolfenstein: The New Order. (And who, according to its credits, pitched in to some extent with this year's even more improbably good DOOM). They've just unexpectedly release a new Quake episode in honour of the dear old man'n'monster-shooter's 20th birthday. It's pretty good, too.
DOPA - not quite sure what that stands for as yet - starts off in the miltary base aesthetic but winds up in that beloved, bizarre gothic castle setting before too long. It's definitely Quake-y, fear not. The first level is structured somewhat like Quake's own first, even repeating the switch 'puzzle', and various nods repeat throughout, but it's pretty much doing its own thing.
Wastes little time in getting tough as nailgun nails too, locking you in a small space with a mini-horde of Enforcers right at the start of level 2. Speed and reflex and clocking pickup locations win the day before long of course, but I definitely don't get the impression that this was made for Quake first-timers. It's busy and ridiculous and secret-packed, and even tries out a few setpiece tricks that I don't believe the original ever did. So it's a tiny piece of good news today.
Here's a direct link to the download - extract the RAR, create a DOPA folder in your Quake directory and stick the PAK in there, then either try the .bat file (I had little luck) or grab a client such as Quakespasm and type
GAME DOPA in the console.