Looks to me like we're heading for a world where branding becomes all-important. Events with limited courses and few facilities but a good name like the "Kent Orienteering League" will do well, one-off colour-coded events with a full range of courses will appear less attractive.
Perhaps this is where the Event Structure Review went wrong. It concluded that the event Level should be based on the quality of the faciities provided, rather than the type of competitor it was trying to attract and what the event would be used for.
Looking at it from a competition point of view then there are:
1) 'Club' events - aimed at the locals, possibly with an informal club league table for good measure.
2) 'Regional' events - generally aimed at both newcomers and experienced orienteers in one region, with results used to generate a league table such as the East Midlands League.
3) 'National' events - which are of a high enough quality to attract people from many regions and could be used for the Future Champions cup, a veterans equivalent, selection races, etc.
4) Major events - ie the British and JK.
Given a breakdown like this it is hardly surprising that it is proving difficult to fit all the events into just three levels.