So maybe, substeems could be common, as tier 1, but the separate token and reward pool is only enabled when an entire community forms around a particular substeem, as tier 2.
For example, say we have a substeem called /s/cn for China. It gets popular enough in its own community that it'd need its own reward pool (and hence, its own token) because stakeholders outside of /s/cn tend to ignore it.
This should allow us to avoid forking into new blockchains.