I think the re-introduction of modrons could tie in nicely with the implied setting's plotline element of the increasing encroachment of the Far Realm into the material world and the subsequent rise of psionics and the appearance of the wilden (further detailed in PH3).
In a remote corner of the Astral Sea, a strange, metallic ball appears, apparently out of nowhere. It lies motionless for a while, but suddenly, with a soft "snick", a panel slides open, revealing a single, large eye.
For a few moments, the eye stares blankly ahead. Then slowly, it looks around, and sees nothing but emptiness around it. It blinks, once, and with a faint whirring sound, the ball extends arms and legs, feet and hands.
Cautiously at first, but with rapidly growing confidence, the creature moves its limbs, flexes its joints. Then, apparently satisfied, the creature stands still. It holds up its empty left hand and a lump of metallic substance appears on it. It holds up its empty right hand and a strange tool materializes there. With precise, regular movements, it begins building another creature like itself.
Some sages speculate that just as the wilden were the natural world's response to the Far Realm's gradually growing incursion, the modrons were similarly birthed by the Astral Sea.
Although no god has claimed responsibility for their creation, some argue that their apparently mechanical nature suggests that they are creatures of Moradin. Others believe that their highly regimented and ordered society points to Erathis or even Bane. A more chilling line of speculation is that they were birthed not to counter the Far Realm, but because the growing influence of the Far Realm is slowly driving one or more of the gods insane. Those who believe this fear that the single-minded obsession displayed by the modrons in their battles against creatures of chaos and madness is a form of madness in itself...