As you noted, there are differing States/Triggers that naturally synergize. For example any of the Damage mitigation types identified in the master table. So with Hammers and Chaos you could combine Evasion, Blocking, and Weaken together. Similarly different kinds of heals will augment each other. Different kinds of States/Triggers will also impact the effectiveness of each type of healing. For example, any of the States/Triggers that boost DPS will enhance Leech healing.
To me the character development system,the previews from dungeons and the puzzle quests makes me look at TSW as a MMORPG where you are rewarded for coming up with ideas and using your head, not just for grinding.
I hadn't realized that you would generate resources for both equipped weapons when using builders. When I did, it blew me away. It's such a neat system and adds so much depth to the builds, it's just awesome!
If you add blood magic to it you could focus on passives that profit from penetrating hits... given that the synergy between blood magic and blades is very strong, shotgun would be merely a third weapon after those two, though. You'd primarily impair or afflict state with blood magic and blades, penetrating trigger with all three, and focus with blood magic and blades.
If you want to focus on shotgun as primary... I see no way to bring a blades in. You'd have to use hammers or elementalism, so you'd use weaken (damage mitigation) as primary state if you use hammers or hinder (crowd control) if you use elementalism... None of them is an option for blades, though. Same goes for subtypes, options would be blast and / or strike, neither of which is possible with blades.
One must still have chaos in oneself in order to give birth to a dancing star.
What worries me the most, is the sheer amount of gear and weapons that will be needed to have multiple decks. I mean sure, it is supposed to be easily managed in-game, I just hope that this is the case.
By "endgame", to really have a good number of builds available to use, you are going to require the same number of gear sets as builds. As well as an appropriate level of gear to suit the difficulty of encounters.