A few hours ago
some random iPad happened to install Rapture from Quaddicted.

Also connected to a DarkPlaces server, so the server browser works.

It also downloaded the map off the QuakeOne maps depot in the process
It's the WinQuake version (haven't summoned the stamina to deal with GL yet ... combine and other stuff and I think lack of clamp_to_edge (?) will be annoyoing.). I wrote Bluetooth keyboard support so I could use the console more easily.
Unwanted challenge: Apparently, ESC on the BlueTooth keyboard exits out to the home screen on an iPad. Trying to figure out if CTRL + tilde or something should open the console, although I plan on making a hotspot on the screen.
Don't plan on requiring the BlueTooth keyboard, I'm more than happy to imitate Minecraft's very functional control layout.

Other challenges I discovered ...
1) Modal messages like the pop-up that asks "Do you want to start a new game?" Haven't decided course of action.
2) ESC key annoyance.
3) Whether or not to use the iPhone's on-screen keyboard or do what PSP Quake did and roll my own. I suspect I may have both be available, but have the latter as the default -- I doubt an iPhone on-screen keyboard is going to autocomplete Quake commands and allow pressing up to repeat a previous command in the history.
4) I guess I'll need to hotspot up the menu items like, say, Spike does in FTE.
Fun discovery ... Quake share doesn't honor the command line. So you can't do "+map e1m1" in the command line, for instance.
Ironically, something that I would be difficult --- sound --- was completely trivial. OpenAL for sound is extremely easy. Trivially easy, really.