Through profane dhakaani rituals or something.

Game has a decent amount of named items that are well, no different from plain magic. Game also lacks crafting system, to big extent. some items to epic and green steel doesn't do much.

we also have a LOT of named items with no sensible value. named items, which could BE of some value, even after level 10 (you wish, i wish, we wish.. not)

as example, we can take kobolds new ringleader:
# Bloodknuckle's Loincloth Waistband - Belt: Light Fortification
# Bloodknuckle's Smasher - +1 Maul
# Brakhash's Axe - +1 Battleaxe
# Bronkarz's Cloak - Cloak: Will save +1
# Grundok's Boots - Boots: Jump +1
# Madooroh's Vest - +1 Leather armor
# Rhakmel's Dagger - +1 Dagger

as we see, besides name, they are nothing special. but what if they were?
i doubt game balance would go mad, overall, if..

the weapons would be tiny bit better than "normal" magic weapons, to make them special, like name says?
like +1 or 2 to damage only?
yes, your flaming starting weapon is better, so upgrade is pointless. except everyone doesn't start at lvl 4 with flaming items.

and it'd be horrible if you could upgrade that belt to be moderate fort at lvl 4 or 5, since level 5 already HAS mod fort items. totally game breaking.
Especially if you'd have to pay for it. (pay the game, not other players)
Heavy fort upgrade at lvl 9 or 11 would also be out of question since it'd wreck the high priced AH market for HF items of that level. definitely ruining the economy.

remember, these are just examples, it could be applied to ALL named items. and named items could be put in ALL quest packs, making doing them more worth while.

now, minimum level for +1 is none. +2 is 2 and +3 is 4, so sayeth the game. (with exceptions but anyway)

what if, named items (and only them, not random loot) would be upgradeable?
so, hit level 2, go to crafting spot or stone of change or what would be used, put in weapon and some collectable things and something more, like money. (oh noes, platinum sink)

and get weapon to +2 (and that damage bonus could be 1d2 now) still not quite over powering random loot, but lot better. (and still better than normal +2 weapon but worse than random +1 flaming or frost weapon)

repeat at lvl 4 (my poor money, i'll never afford it, and how can i find collectables needed?)
and get +3 +1d4 or something.. bit better base damage than elemental weapons of that level but.. lacks that elemental effect, so no abusing monster vulnerabilities to fire or cold or acid or such.

repeat at 2 or 4 level intervals. with end goal being.. hmm.. +10 at lvl 18? (nah, not really, game likes +5 as max besides epic. but past level 8, additional effects could be given, game has a plenty)

end goal is:
named loot, upgradeable. (at decent intervals, not just to lvl 20 epic.)
platinum, usable.
amount of named loot everywhere, increased.
reasons to do odd 3BC quests for that named item, more tempting

possible different upgrade choices? sure. we have fire, cold, lightning, acid, force (exists already up to 1d4), bleeding, and so on damage types.
just possibly limit upgrade to one damage type so that we wont end up with too good items. since it'd be horrible if level 12 alternative to some people would be something besides green steel. (okay, likely not, GS is just stupidly overpowered)

yes, this is all pointless to long term players with lot of good loot already but more recent new players might like the increase in variety.

why, bloodletters knife (a dagger) with bleed effect used to be good long ago. i liked it. now? you wish.