Nothing wrong with Div 6 and 7. I know about 10 years ago BSA was talking about zoning the Div 3 grades into a north and south zone.
I actually quite liked the idea.
Keep Div 1 and 2 for the ten major clubs and maybe call them premier and reserve grades, but if you had a Div 3 north, Div 3 south, or even a Div 3 central, a greater participation rate could result. There could also be feeder clubs too that funnel players into the major club.
For example, let's pick on "Div 3 south" The zone is say South Adelaide, Southern Tigers, Sturt. Those clubs play in the zone league, BUT, you could also include clubs like "Morphett Vale Maulers" or "Willunga Wildcats", or "Blackwood Blockers" Those clubs could also align themselves with the district clubs too.
So what you then have is an area based competition that is a little under "junior state league", but above the social competition run out of a church hall. For near country areas, their rep. team can participate in this league and still play in their local league. Consequently, the level of country basketball goes up too.
It provides a playing path for juniors and ensure the step between social and state based Div 1/2 is not too great.