I just thought about this again. There *is* a problem. The subset stack is not designed to have too many subsets in a row. For every newly added subset, it internally stores the latest index vector for fast removing of subsets. If you add like 10000 of them, that might be a problem.
We have to deal with this. I think a solution would be to have a special mode of the subset stack, where you can only add subsets. Internally it then just replaces the current active index vector with another one (and forgets the previous, so that removing subsets is not possible anymore (gives an error). Could you add that with tests etc? Thats important for this pruning to be memory efficient