Sooooo... here's my puzzler noodle take on the riddle:
In days of yore, quite long before
The humans came to plunder more
This seems to me to refer to the time before True Dungeon became True Dungeon. Back when Jeff was running it as a special Jeff-Con or whatever for his friends and invited guests. This doesn't jive with the next section for context, however, so I'm thinking it is in all likelihood a reference to before True Dungeon became really, really popular.
A relic forged from goods of trade
By ancient hands the thing was made
Seems clear. A relic using trade goods. Likely among the first relics made in 2012 as others have speculated, although something I haven't seen mentioned yet is that the Supreme Ring of Elemental Command was considered to be a relic before the Eldritch classification came around. I doubt that six uncommon treasure-box-only tokens would combine to unlock that recipe, especially since there are so many sets being collected right now.
I don't think the Draco-Lich Claw Charm is a candidate, since it used monster bits and no trade goods.
Regardless, the riddle seems to be referencing a specific Relic.
Alas, for now, the method’s gone
To craft this fine phenomenon
‘Twas fractured by a hand of bronze
And now it’s just some polygons
This section should be considered together for context. The Relic's recipe is expired and cannot be made anymore... "for now." Which suggests that the fragments might unlock the recipe for making it. The polygons says to me that the recipe is an existing relic whose recipe is expired and can only be seen digitally, i.e. can only be seen on TDB, for now. The hand of bronze may just be a rhyming scheme, but a hand of bronze could refer to a clock hand, meaning that time ran out on the recipe, i.e. it expired and now is only viewable online.
So I think this means the relic in question is a specific relic that was among the first ones ever made and its recipe is viewable online.
Another interpretation of "hand of bronze" could be the creation of the Relic Recipe Fragment tokens themselves, if the molds used are bronze or bronze colored. Which makes this line a bit of literary dressing to describe the token making process.
When days are long and three stars bright
The Dark Knight comes with special sight
For bringing forth the pieces all
To eldest place before the fall
Days are long = summer. Three stars bright = over three days.
Dark Knight is capitalized, suggesting some importance to that title. My initial thought is there will be a person dressed as Batman or requires the person with the fragments to show up dressed as Batman. This was dismissed as too silly a premise, much akin to the "go out in a cornfield" idea, but having a person dressed as Batman or more thematically appropriate a medieval Batman cosplay? I wouldn't rule it out.
In any case, this Dark Knight character is coming "with special sight/For bringing forth the pieces all" seems to say that the character is going to be there in the summer for three days looking particularly for people who have all the relic recipe fragments. This character is who we are looking for to give the fragments to in exchange for... what? A Relic Recipe token/voucher, which in turn unlocks a specific relic? Or revokes the expiration date for any relic recipe since the beginning of relic transmutes? My feeling is the latter. You'd still need all the recipe ingredients to craft the relic, but the addition of this Relic Recipe thing opens up the recipe for use.
Eldest place before the fall, coupled with the three days in summer strongly suggests this character will be at GenCon, which also suggests it will be the only place to get this Relic Recipe thing. If so, I think that would be a mistake since not everyone that plays True Dungeon can make it to GenCon, and in fact there are players out there who have chosen not to go to GenCon in favor of the conventions that are more affordable and less crowded. But if it really does unlock any relic recipe since the beginning of relic tokens, well, that could be a decent limiter on it.
So gather now your goods abound
And bring them where the start be found
A myst’ry now that was foretold
With time, that knowledge shall unfold
Goods abound suggests to me the fragments plus the ingredients for the relic. Start be found could be outside at check-in, but more likely the TD Store, which is nearby the start of TD. This also suggests that the Dark Knight character will be somewhere nearby.
There has been plenty of discussion here on the forums about unlocking older relic recipes to be able to get to the Legendary recipes, and Jeff had said he was against reprinting relics but not opposed to functional reprints that do something similar but not exactly. This might be Jeff's way of offering the relic version of the Coin of Mithril Fate. Choose a relic recipe online, collect the Relic Recipe Fragments to get the Relic Recipe token/voucher, turn it in along with the ingredients in the recipe, and boom, old relic created.
Of course, that would be a lot of old relic tokens needing to be made available if the GenCon window is the only window available to make them. And again, really disappointing to those who can't make GenCon. The link on the fragment tokens seems to me to mean their recipe will turn up on the transmute page eventually. And any additional tokens needed to be turned in with the fragments will be made known before then.
I'm probably wildly off-base, but that's what I think.
TL,DR: My interpretation of the riddle is the fragments will transmute into a Relic Recipe token/voucher that allows you to transmute any one expired relic, so long as you have the ingredients for it. Availability of this token/voucher will be at GenCon, and may or may not be exclusively at GenCon, or the player may need to bring all their ingredients for the relic with them to GenCon to transmute for it there and then.
