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.