Nothing like cool mock-ups to get people interested! I certainly think they and the example game will go along way in helping people to understand what's going on. It certainly did for me.
Now, on to first impressions:
Overall - I certainly like the Kin/Tribe idea; it's very fitting of the times. I'd get nervous about some Tribe combinations being so strong that the rest of the board is ignorable, but I guess some Dominion boards are going to being like that regardless. "In games using this" cards are great, but having one on every card is making my head spin a little bit. The are certainly straight forward enough, so maybe with a board in front of me and a bit more time with the ideas, they'd make more sense to me. Do you think any of these can be cut? Or do you think having one, random "Kin Landmark" per game would make the cards function more or less the same way? Again this is purely a first impression.
Mead Hall - I certainly like that at the very least this can trash, but for that reason I think it should cost at least $4, even despite it only being able to play two other Tribe cards. There doesn't seem to be any real setback to opening with this, versus Throne Room where buying it too early means there might just be an extra dead card in your deck. A double Mead Hall opening could even result in you trashing 3 cards before your 2nd shuffle (if they connect). If you're hoping to keep this cost low, I'd recommend dropping the trashing part.
Highland Village - I like the interactions that cancel each other out. So Highland Village initially cost $5 with the setup effect? In a game where the Kin cards are not great, this would be an expensive Village. Making cost $4 ($3) seems fair.
Banner - A victory card that scores off Kin cards seems like a must, but I have no idea how balanced it is.
Gamekeeper - I'm bad at understanding draw cards so I should abstain from commenting on this one.
Telltale - This is quite the Attack against Kin cards. My first thought is that it should have some sort of cap on how many Curses a player can gain. A single card that can hand out more than one Curse per play seems like it would lead too unbalanced play. Of coarse reducing that means the +1 Coin Setup becomes even more powerful. This one makes me a bit nervous, but I'd love to hear if you've played any games with it and how it performed.
Overall - I think the Kin thing is a neat idea, I just wonder if there's a better way to pick Kin cards other than being random. Perhaps some sort of drafting system? Of coarse, as you stated, even bad cards seem to become quite powerful.
Are there more cards with the Kin type? Thanks for sharing!