We do not want to use branches for subiquity. If people want to talk about the policy around their use in Ubuntu they should do that in some other thread
Subiquity has always been a bit of an oddball snap, because it only runs in the live environment which has auto refreshes disabled and so there has been no need for snaps. But 19.04 will add the feature of checking the store for updates and offering an upgrade to the user. So this adds a motivation for the track: we don’t want the user booting the 18.04.3 installer to download a version of subiquity that offers options that only apply for Ubuntu 20.04 or newer and the obvious way of preventing this is to have per-Ubuntu-series tracks.
Part of the reason we haven’t asked for this before though is that this is so far only a theoretical consideration: there have been no changes to subiquity that would not work on an 18.04 system, and more than that, I don’t think any such changes are even planned at this time (maybe @xnox has something in mind here). So we could be “lazier” about this by having all images include and track subiquity from stable until we have a version we don’t want to be offered on older series, in which case we could add the tracks. This would end up in the slightly strange situation where latest/stable would not actually be the newest version of the snap, which would be a bit strange.
If we do go with the snaps, I think track names of “18.04”, “19.04” etc would be fine (i.e. drop the ubuntu- prefix). Also there’s no need to create a track for 18.10, we’re not going to be making new cosmic media again.