...but from what I saw of the changelogs and steves own words its one of the harder parts of the game to develop right.
That makes sense as diplomacy is really strongly linked with how the AI works, which is always a pain to get right. It also explains why the AI is "behind" in so many ways as there are many features that they wont use.
While I would generally agree with the status of the AI, the trade options and diplomacy between player races don't require any logic and besides strings of code to handle the transfers, all is needed is a UI.
Eventually, I don't think that allow AIs to access such tools is a good idea anyway and I actually believe that provided with these tools one could close an eye on the current AI flaws and keep playing with more options at his/her disposal.
While this is listed as a trade update, I would also appreciate such an update as a means of easily managing reparations in a multi-player race game. Coupled with the ship transfer functionality upcoming in 1.14, IIRC, this would be a good way to emulate complex peace treaties between player races. The NPRs of course remain only suitable for wars of extermination but that is what it is.
Yes, that was my point as well. Do not have the opportunity to handle these things is a bit of a pain especially when you go the extra length to create and make your race alive. A race that has superior Lasers could trade for Better missiles without the need to actually research all the techs but will be limited to that one only supply. A trade-based empire could seize all fuel sources with the goal not to exterminate all other races but to force them to trade.
Trading wealth, fuel, minerals and maintenance supplies via the DB is fairly easy if you share the same planet. The other things are more complex, so a UI based option would be pretty cool.
I am aware these things are still possible with the DB edit, it's just an enormous pain.