I'll try to fill in some info about your suggestion,
This was been suggested and discuss by many player and including the participation of some staff too, but answer is always the same, they will not add legendary with total base power above 600 (unless it was rewarded to player like the official tournament) and except from Mew, Celebi (and Jirachi i quess,soon) there will always be ONLY be ONE legendary in each kind, either it posses by staff or normal player.
Before the Hoenn release (and if the server become stable), it was already said that there is already a plan for Auction House
Every trainer have this problem :) but also before the Hoenn release, it was also said that there is already a plan to update the PC storage (not sure thou if "searching" is included in that update)
It would be nice if this is implemented, we can see their evolution tree along with their moves (even if we dont have their seen data)
The trick here is inspect the player info, look in there "Play time" if its above 400+, ask him for help, Mostly you can trust him in terms of trade evolution, and for safe keeping, make a screenshot of the transaction. I really doubt some will scam you and exchange their 400+ playtime for single pokemon.