Indeed and wow that's a long wait, I will have zero chance of running that content in future based on this.
One thing that I think they could do is create some level 50, one star craft recipes such minions, glamours, weapons, special foods, special dyes and even mounts, and have each crafting recipe include at least one material that can only be obtained in dungeons. Recipes could require more than one of the material as needed, or appropriate, and each new material should be unique to the dungeon (and/or the hard version of the same dungeon) it is found in. Of course recipes for consumable items would be most effective since demand would never completely vanish.
This materials should be untradeable and market_prohibited so that if you want to craft the thing, you have to actually run the dungeon needed to get the material - there was something like this in Haukke Manor if I remember correctly. With every second patch, some new craftable items need to be added that use these materials.
Finally, these materials should not be available when running unsync'd, and will be awarded after the last boss fight.
Many will complain of being forced to run the dungeons. Except you're not forced, since the craftable items are entirely optional, and you might even be able to buy the crafted items themselves (not the materials) from the MB.
This would bring some motivated players back to the dungeons. I am sure many would still stay away, but increasing the number of players in this content would help new players and bring older players back to things they may not remember any more.
By adding new craftable items that use the materials with every other patch, SE refreshes the incentive to run the content to get the material. Otherwise as these items start to saturate the player base, the content would die again.
This would also support crafters to some extent as well.
Agreed, but that too is fixable. Level sync was meant to keep older content in balance to prevent overgeared players from ignoring mechanics and the like. Level sync should be tighter to ensure that things in old dungeons actually retain their original sting and danger.