If you held a gun to my head and forced me to make a guess I'd say you could push that approach to order of 100K, maybe 1M documents.
If sqlite had a generic "strictly ascending sequence of integers" type[1] and would optimize around that, you could probably push it farther in terms of implementing efficient inverted indexes.
If sqlite had a generic "strictly ascending sequence of integers" type[1] and would optimize around that, you could probably push it farther in terms of implementing efficient inverted indexes.
[1] primary key tables aren't really useful here.