Zan's proposal is essentially Kuro's proposal w/o a talent tree, but instead of specializing in 1 advanced class instead having the option to go into 2. It also touches on the Title Proposal of having greater penalties for cross class actions. It also introduces exclusives for these advanced classes and forces roles effectively, but ultimately it GREATLY reduces the amount of customization you can incorporate in you character instead of adding to customization which not only does Kuro's idea implement, but so does the Title System even more so. I believe Zan's proposal is the weakest of all 3.

All 3 proposal's define roles, create exclusives, limit actions in a specific way. The main differences is the customization and how things are limited and I believe the Title System is more effective in both.
http://forum.square-enix.com/ffxiv/t...pecializations