I like that idea too...I like this idea, the multiplayer could have a lot of modes. I believe the original UA was designed to be played more online, just see the number of MP maps, but internet in '98 was not ready for this type of thing, so the UA2 could be centered in multiplayer, but with good campaigns, with more history.
And the game could has three modes: Classic Campaign (where do you play as the original UA, but with better updated maps, more units, AI more complex, etc.) Modern Camapign (where all factions battle for the world domination, you would need to defend your territories, etc.) and Multiplayer (with a lot of modes and change of rules, besides user-content)
I don't believe the game need the second mode, but would be nice, because some player want some things more dynamic and with a bunch of changes.
And i like all the Brojnstein ideas and i shall add there shall be not 2 new factions but 3 or 4 new factions...
That would make the game supremely more exciting.
Another nice thing would be single and multiplayer teams.
You know like in some campaigns there are 2 taerkasten fortresses and so they dont destroy each-other but there shall be like Resistance and (a new faction that would like to destroy the aliens and the rebels)it would be awsome.
And even some commands like in some Strategy games there is command that u say 1 in game chat and it says like attack this bla bla...and they attack it...
And even do a "wonder protecting campaign" not truly a wonder is needed but you can do a bionic power source or something like that i dont know...
And as for the weather you should do an eventually changing weather time like sometimes its sunny somtimes its rainy because it shouldnt be all time just sun u would be roasted by now