It depends on the forger. This is mostly an opinion based question some wwill say yes and some will say no. imo it depends on the skill and dedication of the forger.
Gameplay wise, yes. Aesthetically wise... not so much. It may be able to be pulled off, by someone like Felipe Dos, but a visually pleasing map may not be possible. Though that being said, things could be done, like blocking of lifts, or changes in map geometry could drastically alter gameplay.
Sure. It doesn't have to be a completely new map, but you can alter the geometry slightly to drastically change gameplay.
Yes, of course. One thing I did notice about Assembly was the power cores which are plugged in to the walls (like on Snowbound and Construct) can be deleted (unlike Snowbound and Counstruct) which may come in handy when making maps without explosive danger rooms (like the Hammer spawn).
Sure. It is easy to forge something on Sandbox or Foundry, relatively speaking. Assembly is more difficult. Therefore, it is harder to forge something good. Possible? Yes.
Possibly. Those lift blockers could drastically alter gameplay. No map is impossible to forge on, some are just more difficult than others.
It looks like geomerging is an easy thing to exploit on this map. Item wise there's not much avalable. For casual gamers this is a nightmare but for the completative player this would be much more appealing. Weapons could be added. Teleporters could be used for flanks and escape routes. Lifts could be blocked off in order to change the way a map plays. Ahh, sweet sweet forge. XD
Ya I made a kickass conquest map on assembly. I took an area of assembly added some lift blockers weapons and barriers and spawn points and walla a good map on assembly.
Due to the style of the map it is and it isn't. You can create a map that alters its playing style but can't drastically change it or its main playstyle.
Yes, it actually is. I just made a map on Assembly myself. Here, check it out. The description of the map is in the comments on its Bungie.net post.
Well, I've seen one Infection map on it, but I don't think Assembly is really suited for Infection. That's Sandbox's territory.
The word good can be misleading as everyone has their own opinions of good. Good to me could be spawn killing zombies where as good to you could be some featured map that is perfectly balanced and interesting. Know what i mean?