Since 2.0 will be going to a zoning structure, dungeons can all be public(except the story/boss exclusive ones like ifrit and moogle.) But make them like Shposhae(sp?) the low level dungeon. But the solo player or party leader has the option to trigger instance. This provides players who want both what they want. So you enter a dungeon solo see some people fighting but cannot get forward to the boss so they invite you have full group toggle groups instance of the dungeon and take a go at the harder levels then the boss.