What's the story with community repository for Sailfish? Are there any plans about making an official collaborative repo, or everyone expects to use makeshift OBS repos?

This repository can hold libraries and tools which aren't included in stock Mer / Nemo (and aren't likely to be included) and so on. Good examples are additional codecs and support for them in gstreamer (such as VP8 / VP9) and etc.

OpenRepos?

Doesn't look like what I'm talking about. OpenRepos is more of a hub for self contained repos, so how is it different from personal OBS ones? I was talking about a community "contrib" repo for Sailfish which is coherent and integrated (i.e. keeps track of dependencies, consistency with Sailfish releases and so on).

What do you expect it to be like? Something hosted by Jolla or where else? Apologies but I am slightly confused by the question; is it pointed to Jolla or the community at large?

Maybe a more detailed explanation from you could help kick-start something...

This is pointed at community at large but with Jolla in mind. Jolla probably can't officially support it, since they have legal considerations (for example avoiding patent threats). However it doesn't prevent the community and Jolla from synchronizing things. It can be separated into more modular parts too, with "good" (generally risk free) and "bad" parts (patent risky) and so on.

The way I see it is like this.

Let's say you want to package component A. It can't go to Mer or Nemo for some reason. So you submit it to that community repo considering that it has to coexist with other repos in real installations (i.e. that repo has to be synchronized with Mer releases somehow, or have subrepos for them if needed). Then other packages can specify dependencies on that package A if they need to. This potentially can even override some packages from stock Mer / Nemo (example - gstreamer plugins compiled with more enabled codecs). Again - this has to be synchronized, i.e. it shouldn't introduce any incompatibilities.

In other words maemo extras for Sailfish

Easier to install, browsable/searchable/etc catalog.

Also, at openrepos you will be able to create "meta"-repos with cherry-picking of desired apps into single virtual "meta"-repo.

Say:
Alice created appA1, appA2, appA3.
Bob created appB1, appB2 and appB3 (which is forked appA3 with same name, but with different features).

if you enable both repositories, there will be a conflict names/packages/etc.

Charles can create meta-repo called "awesome-apps" and link appA1, appA2, appB1, appB3. so there is no conflict.
When Alice or Bob updates any on linked apps, all users who added ''awesome-apps" as repository will get this updates. Actually this depends on link type: sequential or version.
No unneccecary repsitory updates occures, whenever Alice updates appA3, or Bob updates appB2.

David creates thread on TMO, and states that he created 'sailfish-extras' repo with tested apps. He will link only self-tested and well-working apps here. You enable his repo, and always use tested software. All link are version dependend.

Another example is some-kind of cross-repos dependencies:

Alice created an libA1, libA2 and appA.
Bob created libB1, appB1, and appB2 which uses libA1.

Since Bob personal repository does not contain libA1, appB2 cannot be installed directly by adding only one repo.
So Bob creates meta-repository called, for example, 'appB2-with-deps' and links libA1 and appB2 to it. (now some kind of undefined yet behaviour for default application repo occcures). and when user installs appB2 he actually enabled 'appB2-with-deps' instead of personal repo.

Somewhat compelx IMHO, and it's still geared more for the self contained repos, not for one collaborative community, where coordination is important. Unless such coordinated repo is discouraged, and today's thinking is that everyone should bundle all libraries?

What kind of collaboration is impotant?

Anyone submit apps, somebody accept(reviews) apps?
Maemo-extras style based on votes?
Central (council) coordination on repository content?
Other workflow?

I've created a sailfish_lib user at openrepos which is meant to be used for well tested libs that are used by many apps.

https://openrepos.net/users/sailfishlib

Anyone that knows what they're doing can just pm me and I'll give you the password.