Could be a "somethig" to show who is in the same sector? like "u" but inside the HUD.

Not really a good idea. Such a hud would just clutter the interface more, and it doesn't work well when there are a lot of players in a sector.

I think this could be done unobtrusively. Make the font smallish, have a key to hide it if needed (like what 'o' does), and only show players in the sector. I would use it at least some of the time.

What might be better than this, is instead of showing specific players, maybe just give a summary of how many players from each nation are in the sector. Less clutter, just as much use for determining if you should run for it.