We spoke with a group a few years ago who used OJS in that way, and if I recall correctly, another group who had adapted OCS.
It's not something we're looking to implement in the near future, but I will note that we're putting a lot of effort into building the common elements of OMP and OJS into the PKP shared library -- effectively the two applications are gradually turning into different configurations of the same application. The next big step in this will be releasing the two simultaneously, which is a change we'll expect to make this summer.
That'll hopefully free us up to consider other deployments as well; whether or not we tackle an OCS rewrite for the current generation of our software will largely hinge on this.
Public Knowledge Project Team