There are a couple of issues with the nature of your requests that I'm not sure you're aware of.
A) Adding in custom audio/video
The issues with this is mainly concerned with encoding, transmission from player to player, and the possible content that comes with it.
The thing that makes maps so popular among players is that anyone can play them without needing to download a huge mod, and the map files are so small that they can feasibly be transferred at the start of a match. Audio wouldn't be that much of an issue at all, but video can add a ton of file-size weight to the map transfer. Then there's always the issue of where to put the media, as many people even had issues of where to put the maps with previous CnC games.
The second major issue is that for the feature to be usable, there needs to be some standards known for media encoding; which means that due to licensing it may not include some formats (mp3 or h.264 encoding). The third and relatively minor issue is with content. Should the content of the audio and video be monitored? If they make adding audio and video incredibly easy, I would certainly see griefers taking normal maps and adding potentially-questionable content video on there (ie adult entertainment).
B) More objects to add, especially those not found in missions or existing maps.
Possible issues here: bloat, transmission from player to player, and/or excluding some players.
As I mentioned above, maps excel at making everyone that has the base game able to play them. For that to happen, everyone needs the assets for those new map-editor objects.
If the devs add objects to Generals 2 that can only be found through the map editor (apart from a few easter eggs), that don't exist anywhere else in the game, the first question to ask is why is it there in the first place. Depending on the number and size of these unused assets, it could add a significant amount to the installation footprint (and consequently the download file size) that has no baring on the core game itself.
If you give people the option from either a DLC, a patch or added in with the World Builder download itself, then you're going to start limiting who can play the map...something they won't find out unless they try to load. This could lead to map and map community fracturing.
C) Shortcuts to the game from the map editor
The main issue for this is that both would be running at the same time, and thus both are utilizing resources. There also might be issues of a "live editor" that would need to be mitigated...like how you can make changes on your map in the editor that instantly reflect on the game. There can certainly be a host of errors and such that come about from that.