Overall, I like most of the changes to the trading system in B6.
It appears techs cost more to trade for, which is good.
I also like the fact that you can't dial up the AI each and every turn to chit-chat. That was OP and needed to change. Though, parenthetically, this now re-opens the door for allowing a Diplomacy racial feature like the Terrans had in GC II. Perhaps an DLC or expansion down the road. 
What I don't like is that I can only make one trade per discussion. Most of the time I like making my deals in bite sized chunks, perhaps with give-and-take. Being restricted to only one deal per discussion is not fun. I think we should be able to make as many deals as we like while we're "on the phone" as it were, but once we hang up that's it until enough time has passed.
On the flip side, I very much like the 50 turn limit to many things. Something needed to come in there, and 50 is good enough for me.
Aside from that, I don't have much thoughts on the trading system. At least right now.