I don’t see any downsides to this.
Free-to-play players win because they can purchase exp tomes/skill reset potions/costumes/etc. with silver.
Premium players win because they can capitalize on the demand of these additional TP items.
IMC wins because premium players now have another incentive to purchase TP.
Free players who don’t want to spend, will never spend. Players who ARE willing to spend though, only need to buy enough TP for one of each costume, maybe one reset potion, and enough enchant scrolls to get what they want. They hardly have a reason to spend anymore than that. While they can currently sell tokens, the market will likely be very flooded with competition, as it is in the one and only avenue in which paying players can capitalize. Furthermore, each F2P player only needs ONE token a month. Compare this to the potential profit margins of enchant scrolls. Spenders now have a very big incentive to spend, which is good news for IMC.
This will also address P2W concerns: Right now, only those willing to pay for it can enchant items. If these scrolls become tradable, it will minimize the gap between spenders and non-spenders. Everyone wins!
EDIT: It’s not a big deal if costumes are left un-tradable, if players really prize looking unique. Items like enchant scrolls and skill reset potions though, should definitely be made tradable for the reason above.
Moar edits: Wording and clarification.