Well, honestly I hate the game but that's a tad bit off-topic.

What Jagex is going to realize is that all of the reasons he limited the trading system are going to reappear, and quite honestly the players are going to get sick of the limitations and move on to do something else.
You can basically break a game down into six parts:

1/6: Questing -- Brings on reason to do all of the following, and gives EXP
2/6: Grinding -- EXP gain, usually coupled with Farming, because you get money/items from each kill as well.
3/6: Farming -- Financial/Material gain, usually coupled with Grinding because you get EXP from each kill as well.
4/6: Commerce (trading, buying, selling) -- Allows players to buy shop items or obtain rare items they might not find on their own.
5/6: Politics -- Clans/Guilds systems promote group quests, group farming, group grinding, group PVP, and gives the players a sense of togetherness, like they're part of something larger than themselves, even if it is just a game.
6/6: PVP -- Kill the opponent because you have better gear/a higher level, or be killed by the opponent because they have better gear/a higher level, then whoever lost realizes they need better stuff, and does the first 4 parts of this list, usually with the help of the 5th

Unless a game has ALL of the above, it's really not worth bothering with. Each one works together, in a sort of way.

Runescape will never be as fun as the old style one was. My opinion but it's way to childish now.

I agree with Silence and Lockem, However it bringing the free trade back will also reel back in a lot of players, however it will bring back a lot of the damned scamming that many trolls had fun with.