Apart from reducing cost and travel time, regional leagues would help foster local rivalries, which could raise attendances and revenues. We already have regional leagues at lower levels so the question here is whether we change the number of national leagues at the top. Change could make the clubs at lower levels more stable and help maintain the deep league structure. It's certainly not unreasonable to revisit such questions occasionally.
I think making leagues one and two regional and only having two national leagues at the top is too much of a change. There might be a case for regional leagues replacing league two and the national league. This would be complicate by it involving two different league bodies, needing an expansion or reducton the EFL or a rejigging of the NL and feeder league, which is probably too political to succeed. As an aside who thought National League North and National League South makes any sense (its either national or not)
I'd create a PL 2, also with 18 teams, to basically replace the championship. Less filler should make the matches more interesting and they could have breaks for internationals as well.
League 1 and 2 should be reduced to 20 teams and league 2 could have two regions, giving us 96 teams instead of the current 92.
Fewer matches probably means a slight increase in ticket prices, but atendances could potentially improve on weekends to offset the lost midweek matches. Higher quality matches could also mean a better tv deal and travel costs could be reduced for fans of smaller clubs.