I've always favoured the north and south having separate 4th divisions. Not just the cost of travel for the clubs and the fans saving aspect but the attraction of playing more local teams, as opposed to travelling hundreds of miles to games
Doesn't always work as you imagine. Lucky for those living /playing in roughly the central band of the country (Manchester & Leeds to Birmingham ish) but my Blyth's experience in the Conference North included Kings Lynn, Histon (outskirts of Cambridge), Bishop Stortford, Redditch, Solihull (both goodly south of Birmingham) & Gloucester-playing at Cheltenham Town's ground. Even the Northern Premier League we're now in has teams in and around Birmingham & Leicester that are too far north for the Midland League to accommodate.
Our nearest games from a coastal town north of Newcastle generally have been Workington on the opposite Cumbrian coast or Harrogate. Largely due to the Northern League's isolationist stance against supporting the pyramid and resisting clubs promotion which Manchester, Yorkshire, Midlands etc based feeder leagues embrace.
Luckily last season Darlington were on their way back up towards their lost league status & now we have Spennymoor coming back up after some poor financial fortunes last time at our level so theres been a couple of near as local derbies
The trouble is that the south of the country is a narrow wide strip with a lot of teams spread widely across a flat area so the north effectively does become pretty much everything above the M25.