A problem people are often pointing out now is that with the new training system Tria and PP will soon be both useless. How about having a magical vendor of some sort to spend PP (and an appropriate amount of Tria) at to get interesting items like rings or neck items that increase specific skills or stats, or special uncraftable potions. Perhaps an item you can use to gain a special buff like, say, +20 sword for 10 minutes. Personally I'd love to see the neck and ring slots be useful. Even the extremely rare Ring of the Past is underpowered compared to the current stat caps.
As far as making this fit into the story, you could say this vendor learned how to take the "essence of learning" from people and channel it into items to further increase their power, and then the Tria is a cost for this service. You could then have "Crystal of <stat/skill> Essence"s, which would raise a stat or skill for a time. These buffs should either be more powerful or more long-lasting than ones you can get through potions and the like, because they are harder to obtain; I'd prefer longer-lasting but lower strength personally. This would provide incentive to actually obtain them. You could even make some interesting ones that apply effects like a small movement speed increase or cause your weapon to deal additonal Way-aligned magical damage, or even just some cosmetic ones that give you an aura of some sort.
Similarly, a sink for excess Tria will certainly be needed, and a vendor like the above might be appropriate. Perhaps they could sell (among other things) special, unenchanted neck and ring items that the magical vendor could then infuse with "essence of learning", making something of permanent power but at a much, much greater cost. This would not be a game-changer in the sense that people can all of a sudden carry 3000 weight and smite dlayos with a single hit, but it would give a way to drain the economy of excess Tria and give the players who want them something else to shoot for and then play with. As I've learned from various other MMOs, players like shiny things!
The benefit of adding these vendors, apart from initially keeping Tria and PP from becoming useless, is that their inventory can be expanded over time to include other desirable items, potentially special glyphs, cosmetic items, furniture, magical weaponry... this way, there will *always* be some sort of goal for players to strive for, and will keep the Tria from becoming worthless.
If this sort of system is considered seriously, I'd be willing to devote some of my time in helping to create and test it.