That's pointless when I can pop 4 castles up the way in a day or two, and get 10 times as much land with just 1 player, plus get the neutral cities in between, which is something the single tile claims can never do. I spent the last couple of days filling in the south castles, that will be finished by tomorrow then I'm heading north. I might fill in a few castles on our north edge, then I'm going to do the eastern edge. This makes spot land claims kinda silly since they'll be swallowed up by castle gains within a week. So we have reason #1 against that plan: it will be obselete as soon as the castles go up.
Anyway, joining up Bearfort with a land bridge that must be maintained doesn't actually get us anything at all, since TTHSK the mayor of Bearfort isn't actively playing. So we have reason #2 against the plan: it doesn't gain us anything. So in other words, even if we weren't going to have castles up that way pretty soon, you haven't outlined any benefit the plan gives us.
Even with a dedicated map system with special markers and repeatedly mentioning it, many people still haven't got the message about where the best place for garrisons is, do you really thinking that micromanaging everyone to do land claims is going to work? Reason #3: it's hard enough getting people to coordinate with basic stuff, so micromanaging people to do single-tile land claims won't be a realistic proposal.
Going from Skr's (Greens) experience, he linked up the green areas for quite some time via land bridges. This had no effect whatsover on him controlling cities. See the city of Kingspile. Dominated by a green castle for a long time, linked for quite a while to his capital by land bridges. We put a castle in and it instantly converts to us. He spent a lot of time maintaining a land bridge and it didn't do fuck all to help him hold cities. I'm calling manual land claims as a broken game mechanic. You don't get XP from doing the land bridge thing. We need people high enough level to build garrisons rather than waste turns on make-work.