In the Civ system, each tile had a % weight associated with a tile's loyalty to a given race. Perhaps something like this also has to be considered for FE. Thoughts must be given to the three types of ZofC interaction: City - City, City - Outpost, and Outpost - Outpost. While not perfect, here are some ideas to address this:
Yes, this was a good way to represent the shifting control of borders and gave you some warning when a piece of land you currently control is under threat from your opponents' expanding influence, and lets you know that you need to do something to prevent a non-hostile takeover of some of your territory. That said, though, I don't think they should COPY this system, because if I want that system, I'll go play Civ IV.
If an outpost has the same faction ZofC on a given side as well as opposite that side, then the outpost flips.
If an outpost has the same faction ZofC on three of the sides, then the outpost flips.
Of course! If it's being squeezed by two enemy towns, then it should flip. This will also prevent the AI spamming random stuff behind your villages. However, I don't really get how your second criterion differs from your first. If you have the same faction ZoC on three sides, you must also have the same faction ZoC on two opposite sides, making your first one sufficient for flipping...
This strengthens the need to have contiguous ZofC throughout your empire as being 'flanked' culturally could leave you with less than you've bargained for.
This. I think one of the best institutions in this game is that 15% unrest hit for not being connected to your capital's territory, representing your people's loss of motivation for being a "provincial" town, or as I like to think of it, the fruits of rampant corruption and mal-governance in a village not adequately linked to your empire's beating administrative heart of power.
Although I sometimes employ city "snaking" to link up my cities' ZoCs (I avoid it where possible, but sometimes settleable spots are just too far removed from each other, over a mountain and 30 tiles away, and outposts with their small ZoC and heavy early game cost just don't cut it, especially for my second city), I think a contiguous empire is crucial to a budding empire, as it makes you think more carefully about city placement and forces you to develop and expand your early towns to prevent rapid expansion.
Though, Firefly, to be honest, considering the fact that outposts can be flipped and cities can't, and taking into account how generally underpowered outposts are at the moment (the upgrades aren't worth a whole lot, and they're exceedingly vulnerable), if you just build a city near a chokepoint instead, it almost always does the job better. I like your ideas, though, but I would add that I think outposts need a little more love than they currently get for me to consider them more strongly for use.