Oookay…

After a search, I found one way to do it:
sudo apt-get install timidity tuxguitar-jsa
This installs a real-time sequencer.
Tweak the settings in TuxGuitar (F7 -> sound) to use this, on the appropriate MIDI port — in my case, Gervill.

1. Will it run under Ubuntu?
   That’s kind of paramount for me…
2. Will I actually use it?
   If people are going to spend money on my behalf and I get a say in it, I’d like to make sure they get value for money.

The first point is easily settled with a quick Google… except it isn’t. As in: the company says “yes”, plenty of users complain. Hmms. But, in the course of googling, I stumble upon TuxGuitar, a freeware project doing roughly similar things. (Note that development seems to have ceased 3 years ago…). Installed it, but: no sound. For a tablature editor (or any musical score editor, for that matter) lack of sound is of course the death knell. Tweaked around with the various settings, unplugged and replugged cables, but to no avail. Left it alone for a long while, and then realised I didn’t do the obvious: complain to google. I do, and indeed, the first hit solves my problems! Turns out Ubuntu doesn’t come with midi support by default. Makes sense, probably. Anyway, let’s add some!

In a nutshell: install TiMidity, a piece of software so finished it hasn’t been updated since before 2005 ;-). Then, run TuxGuitar, tweak the settings to use a TiMidity midi port as output, test, et voila! (In case of absence of Voila!, choose a different midi port and repeat).

Now to find out what this TuxGuitar thingy actually does…