Thanks for the idea! I like it, but I don't think I'll add it.
Two reasons for that come to mind: First, while teamwork is important, you can't expect everyone to actually DO that. In other words, if a spot on the map is taken by the team, people will place their dungeons there as soon as possible, and not a dungeon the whole team agrees on. You could get around that by having people in the team vote on what dungeon would be placed next, but that'd add another layer of complexity. Second, that'd also makes unfair dungeons more powerful (this time around, the dungeon-selection should be more intelligent, and thus better suited to pick out fun dungeons most of the time, ignoring the unfair ones).
However, there is still a visual competition. Aside from story events, which may even include something like that (the ones we've planned now don't, but again, I do like the idea :)), there's the option to buy towers. Those boost the stats of your team. If you're level 10 or higher, you have a rare chance of finding tower blueprints in a dungeon. If you do, your team can build that tower - though they are very expensive, and it can only be build if all players in a team work together on that. You can also pay spies to bring down the enemy-towers. THOSE are shown as graphics, and that allows some degree of visual competition.
Though I do like your idea. Maybe we'll add it as a pure visual indicator, with no real gameplay consequences, or as one of the weekly events.
Perhaps this post will get me points for originality at least.
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