Much stuff here. Bear with me or just comment on how boring I am but don't nitpick on the first point without reading everything.
- Remove arcade tab from mission interface
- Remove Coliseum from UI
- Add haven tab to mission interface
- Town Square
- Bazaar
- Garrison
- Arcade (as a location, not portal)
- Make GvG accessible only from the GH
- Create four Coliseum entrances in the arcade (one per tier LD and one for BN)
- Block non-usable loadouts upon entrance (instead of the current marking mechanism)
- Modify mission layout to make for easier viewing (tough to keep "nonlinear")
More to be done. This is just part of my train of thought. The other caboose is coming once I finish counting sheep.
"Make GvG accessible only from the GH"
Fine, as long as we can leave after we've signed up. GvGs can take a while to get going, and it's often helpful to go around haven looking for opponents.
"Create four Coliseum entrances in the arcade (one per tier LD and one for BN)"
This seems a bit tedious. Maybe something like an extention of the arcade(building) to the left, near Sullivan, with one signup console and some decorations? The coliseum signup UI for LD could be slightly redesigned: one button for each tier, with the buttons above your clearance level grayed out. The GvG button could be removed if GvG signup was in GH only. The spectate button could be removed too, and a second console could be added to the aforementioned room that brought up the spectator UI (which needs some rework too, grid layout perhaps?)
"Modify mission layout to make for easier viewing (tough to keep "nonlinear")"
Hmm... Since you don't have any specifics, I'll make some up. xD
Change the mission selection screen to more resemble the arcade gate map. Have each group of missions (2-1, 9-3, etc) in rows like the rotations on a single CW depth, and when completed they would unlock the next rank up, which would be below in another row. This gives it the "talent tree" feel of unlocking more missions as you progress, but at the same time maintains the nonlinearity of being able to do any mission in your sub-rank in any order.
The window would be the same shape as the arcade console, only mirrored; map on the left half, options on the right. When the window is opened, the left half would be blank and the right would have the "mission, prestige, expansion, haven" options. If you choose anything but "haven", the left would be the new mission map thingy, and the right would have the description, rewards, difficulty, party options, and start button. If you choose "haven", there would be the options (square, bazaar, garrison, arcade) on the right, and either a blank left or a gate map with the haven clockworks symbol. Or maybe an actual map of haven :o
P.S: addition to OP: add the Lab to the "activities" tab, and make the party finder only accessible from the arcade.
P.P.S: maybe make missions only accessible from the arcade as well? Maybe. Don't like this idea as much.