Its certainly not unheard of to have such systems in RTSs. I've played numerous ones which have allowed the donation of units and buildings aswell as resources.

Would be interesting to see how larger scale trading would impact on diplomacy and the game as a whole. Certainly, in online, it would help protect weaker players and people could work cooperatively, being able to donate planets which would be more of an advantage to a particular player.

I may be borrowing it a bit from Civ4 where you could demand/buy/trade cities for other concessions.  In terms of Diplomacy, I figure this would be a huge concession towards an AI to get them to consider a Cease Fire or Alliance earlier on.  For multiplayer, an ice planet for a player who has only volcanic planets might be a good bribe to get them to do something for you.

If it's single player, it'd be an AI Diplomacy factor like when you give them money or resources - It boosts them by 10% (max) favor and it slowly degrades over time.  Since you'd be handing over a planet, I would assume that this boost would be more than 10% - Say closer to 20% (max) for a good quality planet.

For multiplayer, you never know as most of the times you have to rely on things in good faith.  If you're playing with a good friend or two, this would be a simple way to ensure everyone gets an even distribution of resources (metal/crystal).  Currently the only way to trade a planet is to abandon it and allow a friend to recolonize it.

Trading planets isn't on the slate for Diplomacy, sorry.

Why oh why don't you listen to your customer Stardock/Ironcled?? Many of us asked for more trading options way back when Sins was first published. Having just the option to trade resources is not worthy of an 4X game! (not even worthy of an RTS nowadays)

Oh you'll get some trading, but nothing that's against Sins canon.

actually if you look at things like star trek voyager - trading essential parts of tech is not done, therefore the vasari woulkd be unlikely to trade their phase milles or gate tech.

This feature definitely gets my vote!
I don't care if you think it's against the "Sins canon". I play multiplayer games for the teamwork, but Sins doesn't have enough teamwork options. I've wanted this feature since I first played Sins online, and was really hoping this would be in Diplomacy. I can't really think of any other diplomatic feature that would be as important as this one.

Another related feature that should definitely be available:
Shared resources for teammates. All credits and resources are divided evenly between the team.

In Sins, all the human (Trader) worlds are independent and have their own forms of government (the neutral worlds). Some of the larger ones control multiple planets, whereas most are solitary. When the Vasari arrived, the Trade Order realized that they had to form a tighter government for mutual defense or face extinction - which is the TEC (Trader Emergency Coalition). By the time of Entrenchment and Diplomacy, the Trader worlds are realizing that the TEC is becoming so powerful that it's overriding their soveriegnty (as you know from playing, it's submit to TEC will or get bombed into it ).  It's roughly like when Rome stopped being a Republic because Caesar took power and didn't give it back. Certainly the populace of those planets, who feel they should be ruling themselves, probably wouldn't appreciate being traded like chattle.

For Advent and Vasari, while they're all of the same race respectively, much like the TEC they represent different factions of the same overall group. They fight against one another at times, even though their overall goals are the same.

All right, that makes sense. Thank you for clarifying.