If numbers continue to dwindle, I'm happy with all countries in a continent in one league structure.
Or just the entire world as one country, but you continue to play with your flag beside your team name and draft in your country, however that would work. Several "top divisions." Fill I.1-IV.64 then another I.2-IV128 then another I.3... etc. Promoting or demoting you can go into any branch (I.1 branch, I.2, I.3, etc)