For the MP stuff, I'm fairly sure the events that take a country as a parameter cannot accept the <Player@X> logic (they actually get a country number 4475 - 4482 representing starting point 1-
...using them gets no trigger fired. For reference, these are the events that take that parameter along with a link to DeeZires online info on how events are coded in a map:
http://www.deezire.net/modules.php?name=En...=content&tid=22
5 = House Discovered By Player - e.g. 5,0,[house number]
9 = All Units Destroyed - e.g. 9,0,[house number]
10 = All Structures Destroyed - e.g. 10,0,[house number]
11 = House Completely Destroyed - e.g. 11,0,[house number]
17 = No Factories Left - e.g. 17,0,[house number]
18 = Civilians Evacuated - e.g. 18,0,[house number]
25 = Horizontal Axis Crossed - e.g. 25,0,[house number]
26 = Vertical Axis Crossed - e.g. 26,0,[house number]
29 = Attached Object Lost - e.g. 29,0,[house number]
30 = Low Power - e.g. 30,0,[house number]
35 = Object Detected By Searchlight - e.g. 35,0,[house number] *This also needs Search lights working
44 = Object Is Attacked - e.g. 44,0,[house number]
53 = Houses Spy Enters - e.g. 53,0,[house number]
55 = All Naval Units Destroyed - e.g. 55,0,[house number]
56 = All Non-Naval Units Destroyed - e.g. 56,0,[house number]
58 = Power Full - e.g. 58,0,[house number] (Yuri's Revenge Only)
I believe actions do accept the countries from the <Player@X> logic, the following is a link to DeeZires info on Actions and the format for the change house (country) action that I know works.
http://www.deezire.net/modules.php?name=En...=content&tid=23
14 = Change House - e.g. 14,0,[house number],0,0,0,0,A
This logic would also really need the [Triggers] section in a map to allow a trigger to be owned by a Player@X player rather than just a country (first player on the map as that country gets the trigger), Neutral, Special or <none> for no owner (sound effect triggers and such).
On the topic of the SensorArray logic, a SensorArray will still detect subterrranean logic units burrowing under the ground and will play a radar even when a unit with sensors detects a cloaked unit in range (though it won't detect the cloaked unit itself) and when it detects a subterranean unit. However there are no EVA events associated with these which I think there should be.
As for what is still needed for additional multiplayer sides, the game still needs to be able to use additional taunt files or at least made able to be told what existing country to share with. Taunts are held in a subfolder as .wav files in the RA2 folder.

http://www.deezire.net/modules.php?name=En...=content&tid=22
5 = House Discovered By Player - e.g. 5,0,[house number]
9 = All Units Destroyed - e.g. 9,0,[house number]
10 = All Structures Destroyed - e.g. 10,0,[house number]
11 = House Completely Destroyed - e.g. 11,0,[house number]
17 = No Factories Left - e.g. 17,0,[house number]
18 = Civilians Evacuated - e.g. 18,0,[house number]
25 = Horizontal Axis Crossed - e.g. 25,0,[house number]
26 = Vertical Axis Crossed - e.g. 26,0,[house number]
29 = Attached Object Lost - e.g. 29,0,[house number]
30 = Low Power - e.g. 30,0,[house number]
35 = Object Detected By Searchlight - e.g. 35,0,[house number] *This also needs Search lights working
44 = Object Is Attacked - e.g. 44,0,[house number]
53 = Houses Spy Enters - e.g. 53,0,[house number]
55 = All Naval Units Destroyed - e.g. 55,0,[house number]
56 = All Non-Naval Units Destroyed - e.g. 56,0,[house number]
58 = Power Full - e.g. 58,0,[house number] (Yuri's Revenge Only)
I believe actions do accept the countries from the <Player@X> logic, the following is a link to DeeZires info on Actions and the format for the change house (country) action that I know works.
http://www.deezire.net/modules.php?name=En...=content&tid=23
14 = Change House - e.g. 14,0,[house number],0,0,0,0,A
This logic would also really need the [Triggers] section in a map to allow a trigger to be owned by a Player@X player rather than just a country (first player on the map as that country gets the trigger), Neutral, Special or <none> for no owner (sound effect triggers and such).
On the topic of the SensorArray logic, a SensorArray will still detect subterrranean logic units burrowing under the ground and will play a radar even when a unit with sensors detects a cloaked unit in range (though it won't detect the cloaked unit itself) and when it detects a subterranean unit. However there are no EVA events associated with these which I think there should be.
As for what is still needed for additional multiplayer sides, the game still needs to be able to use additional taunt files or at least made able to be told what existing country to share with. Taunts are held in a subfolder as .wav files in the RA2 folder.