yes i do think they should gain a ranking system for the GTS.
i also think nintendo missed a trick in not enabling you to see what OTHER people want.
what i mean is, say i have a level 60 steelix i want to trade, i could search on the GTS for people who want a steelix, and see what i could get in trade back.
that would really aid it.
i also think a unfair trade rule, if nintendo added a level gap system, maybe no trade can take place with 2 pokemon that have level gaps greater than 25 or something, stopping people from asking for a level 100 rayquaza for a level 1 bidoof, lmao.
i also think a option to almost "bookmark" a trader would be nice, if you find a trader that seems to do good trades, you could almost subscribe to them, so when you log into the GTS you get informed of any new pokemon they have put up for trade.
these are my ideas for a future gts :)