It may be too optimistic but I still hope that they will open up more parts, given all the push from the community, e.g. some apps (email for instance). However, not everything for sure...

The additional problem is that when Jolla did open the browser because they knew they needed more resources to get a better browser. Not many community people contributed back. And that justified likely some of the internal Jolla voices (mainly the investors) that asked to keep it closed as they mainly see the cost of opening. I am sure that the OS opening will be easier with much more community contribution which would show how useful it can be.
Outside of the porting to devices, and from my non-developer view, I mainly see a couple of guys actively participating in code contribution...
It is again a chicken and egg story because the community is probably small also because not enough stuff is opened.

Again I hope they will open some parts in 2018 because I fear the small community could get even smaller