> The problem is that distro package managers are many and often complex to satisfy, which is one of the reasons people don’t develop “real” desktop software for Linux.
If by real you mean the kind of proprietary {ad,spy,toolbar}-ware encrusted "real" desktop software that Windows has become notorious for then I think we may be better off without it. If you're talking about OSX, then I think you're missing that it's a market skewed towards those with the money and will to pay for proprietary software. Plenty of people are developing "real" desktop software for Linux.
> The new generation of installers (flatpak, snap etc) takes a cross-distro approach that is supposed to result, more or less, in “package once, run everywhere”: you build your app in a certain way and every distro should be able to run it, regardless of package managers. It’s basically a way to offload the compatibility headaches to flatpak developers and distribution builders.
This isn't novel. 0install and AppImage have been around for a while now. What is novel is that Flatpak combines this with sandboxing that doesn't really do so much to mitigate against any vulnerabilities that aren't in the kernel. I actually think they've got the sandboxing right, in that they are really starting with minimum privileges and adding only what is needed.[0] The problem, as they state, is that it is fine to drop all privileges for something like a single-player game, but it sucks for a file manager. At least according to their wiki, they're already doing most of what you could imagine you could improve on the sandboxing. [0]
It's always this interaction with the outside world that breaks sandboxing. It's rather easy to make a sandbox that runs as nobody and has no privileges and no capabilities and no file access. It's a bit harder to make something which has any of those things in a way which the user can grant sensible permissions.
It sounds like in Portals [1] the Flatpak team have gone in pretty much the only workable direction, although the Wiki is hopefully out of date and there are more portals. The problem they will have found is that to package anything useful and get feedback and validation requires that they implement the most difficult bits first. So I suspect the situation is "secure file picker is coming".
Sandboxing is a lot of work, not in the closing down but in the opening up. One of the more innovative approaches is to be found in Sandstorm [2]. Although marketed as a way to run web applications on your own server easily, it is actually a tight sandbox built on top of Cap'n Proto, which means that E-style capability-based RPC is intrinsic.
Sandboxed apps have no access to anything, cutting down on kernel attack space. The only connection to the outside world is through a UNIX socket file descriptor opened by the supervisor. The capabilities-based security model mean that a sandboxed app could request the ability to connect to "drive.google.com", or even a specific URL. This could also be passed to other apps through the supervisor, subject to user approval. Capabilities can be stored on disk to be later restored from the supervisor.
In Sandstorm the UI for granting capabilities between apps is working, but progress has slowed as the team have all had to find other ways to pay the bills.
> Obviously that approach works only if flatpak does actually get good support in all distributions and becomes a de-facto standard, which is a challenge because there are many competitors (Ubuntu Snap being the most relevant one). If it remains just a glorified rpm (i.e. a redhat-specific tool), then there is no point.
I think the problem is that if your target is casual users, they're not going to necessarily understand the nuances and limitations of the sandboxing.
[0] https://github.com/flatpak/flatpak/wiki/Sandbox
[1] https://github.com/flatpak/flatpak/wiki/Portals
[2] https://sandstorm.io/how-it-works#capabilities