Open Game Updater.
Let it update the install and get disconnected from steam.
Log back into steam and start the game.
Now you can not select Tanoa in the Editor as it is still locked.

You can place Apex Objects in the editor.

The game is installed under %steamroot%/steamapps/common/Arma 3 [development].

The game is started with Apex. RPT Log:

11:39:55 ============================================================================================= List of mods ===============================================================================================
11:39:55 modsReadOnly = true
11:39:55 safeModsActivated = false
11:39:55 customMods = false
11:39:55 hash = '1114C9AC3E71B75642E569C90E55C20122D09722'
11:39:55 hashShort = 'b5c2ca7b'
11:39:55 name | modDir | default | origin | hash | hashShort | fullPath
11:39:55 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
11:39:55 Arma 3 DLC Bundle | dlcbundle | true | NOT FOUND | | |
11:39:55 Arma 3 Apex | expansion | true | GAME DIR | 8cdfe4aefef5c3473b8d29c7fca15e34a18026ec | 1884a207 | D:\Program Files (x86)\Steam\steamapps\common\Arma 3 [development]\expansion
11:39:55 Arma 3 Marksmen | mark | true | GAME DIR | c4179d8a0b399f5b0cf5f9430c089c9ced900a51 | e9b4d6f3 | D:\Program Files (x86)\Steam\steamapps\common\Arma 3 [development]\mark
11:39:55 Arma 3 Helicopters | heli | true | GAME DIR | 3ee55b78b11123fcdac52481db2f0e696b33f1fc | 9019ea85 | D:\Program Files (x86)\Steam\steamapps\common\Arma 3 [development]\heli
11:39:55 Arma 3 Karts | kart | true | GAME DIR | 0d5caa8868adc86ecef1167f745daff6c1c94df5 | 3ff5f268 | D:\Program Files (x86)\Steam\steamapps\common\Arma 3 [development]\kart
11:39:55 Arma 3 Zeus | curator | true | GAME DIR | 525e4b56c087305cd405859cfc5bbd527f01b805 | 6c6a9d4b | D:\Program Files (x86)\Steam\steamapps\common\Arma 3 [development]\curator
11:39:55 Arma 3 | A3 | true | NOT FOUND | | |
11:39:55 ==========================================================================================================================================================================================================

Also from the RPT:

11:40:15 Starting mission:
11:40:15 Mission file: tanoa_intro1
11:40:15 Mission world: tanoa
11:40:15 Mission directory: a3\map_tanoa_scenes_f\scenes\tanoa_intro1.tanoa\
11:40:18 No more slot to add connection at 015030 (1523.6,3012.8)

Full RPT under:
http://pastebin.com/WRrJd8C8