Can't see this working in FFAs, only two-teams games (1v1, 2v2, 3v3...).
It should only apply to situations where all players can see a territory
...AND the territory is owned by a player.
Otherwise, let's say:
Pretend this is a map:
{A}{B}{C}
Let's say a player (1) is in A, and a player (2) is in C. They don't border, so neither of them can see them there. Players will meet as soon as 1 or 2 hits B, and they'll have a double surprise encounter (none of them was aware of the other's location).
With this spectator mode where you can see what territories everyone can see, you'll be able to see "B" is a neutral, and has x armies on it.
With an alt/friend/whatever, it'll NOT be a double surprise encounter, because 1 and 2 can both see it on spectator mode and find out the enemy is in the opposing territory.
~~~
Beren's idea (...AND both players know everyone touches it) gets probably too confusing or even impossible to code properly. How can you judge that 1 knows 2 is in C, or 2 knows 1 is in A? Let alone judge both at the same time?
~~~
It gets even more confusing in 3-man FFAs and larger. Using the same old map except a bit larger:
{A}{D}{B}
{C}
Player 1 in A, 2 in B, 3 in C. D is a neutral territory.
1 is unaware of 2 and 3, and vice verse, but 2 and 3 are aware of each other.
Assuming 3 takes D. 1 and 3 will be aware of each other, but 1 and 2 still won't. On the spectator mode, 1 will be able to see D visible and will therefore know 2 is nearby. Same goes for 2 knowing about 1.
EDIT: Changed every [] to {} because I forgot [] + B would make stuff bold...
Edited 4/27/2016 19:49:23