With the advancement of technology that can be used with magic, I would expect that complex magical items would come into being. Even though this idea results in things that are very to obscenely expensive items, it should be useful in all editions, retroclones and even some other games.

A complex magical item is simply one made of more than one part, each with a different enchantment. This isn't like staves, which hold many spells, but rather enchantments that work together to create a single effect or, as the idea matures, a very few effects. A simple siege weapon example:

The blaster cannon is effectively a giant wand. It casts a maximized fireball, an admixture fireball/electric ball, an admixture fireball/sonic ball and disintegrate as a single effect (and all at higher caster levels than the minimum). So anything that isn't turned to dust by making a save versus the disintegration is probably burnt/shocked/vibrated to a small pile of ash. It has four components plus a command part. The last uses a synergistic feat (like the one in Kobold Quarterly 18). Without the command part, it can use only one of the effects per round.

If used with a rod of lordly might, all of its functions may work together...

Of course it can be used for much more than combat. A good example of that is a lyre of building that has parts for a weakened version polymorph any object that only converts non biological (actually non creature so as not to affect undead and constructs) matter, hightened stoneskin and resist elements. It makes furnished buildings that are twice as tough (hardness, hit points) and as energy resistance 10 to all energies. It can make wooden buildings that are effectively immune to rot, termites, most fires and weather. These buildings may last for centuries, if not millienia. Makes the extra espense of the lyre worth it for how much the owner can charge others for such structures. Throw in fly or levitate and it can make floating buildings (fly allows it to move rather than sit in one place). Add airy water and surface dwellers can live inside the structure underwater without fear. Add create air and make spelljammers that never have to worry about the envelope's quality. Add rope trick or dimention door and reverse gravity and then it starts to get weird, at least geometrically (and with DD, the building may be spread out). And finally, gate allows for a building that can sit in more than one plane at the same time.

I would expect that complex magical items would come about when clockwork is invented. Each part could have its own enchantment and allow for rather powerful effects in very small objects. What makes it even more powerful is that the parts can be changed out. Replace the part that casts haste with one that casts time stop and combat becomes much more interesting for those fighting the watch's owner.

Another, based on that issue of KQ, merges black tentacles and acid arrow. What is different about this device is that the arrows are admixtures of all the energy types (so 5 times the normal damage) and there is a maximized admixture fireball/sonic ball that goes off once the last tentacle is destroyed or the spell ends.

Magic missile plus obscuring mist plus ray of enfeeblement plus reduce (the missile is there to extend the range of the others more than to do damage) results in a target that very short, weak and lost in a fog. Throw in a metamagic feat that allows conditions to be added and things like fatigued, confused and nauseated come into play. Considering that all the spells are first level (sans the metamagic feats), this is a rather powerful effect for the potential price.

And then there is the devices meant to keep the dead dead. Stone to flesh plus trap the soul keeps the target from being raised and makes undoing the petrification much more difficult. Or stone to flesh plus polymorph any object turns the body into black stone, a substance that has traits of jet and tar. It can not be returned to flesh and life with a simple dispel magic or anything else less than wish/miracle. A death spell plus destruction and slay living also makes returning to life almost impossible, the difference is that it takes more than a wish (i.e. an epic or 10th level+ spell).

Another use with the lyre includes plant growth and fabricate. Use tree seeds and one never has to cut down a tree to for raw materials. Add in a stabilizing spell (say 6th level) and one could make a fort or castle that sits still on the ocean. It stays where it is and with stoneskin, it is very impact resistant (double hardness). With a solid water spell (say 5th level), the fort could be made from sea water instead of algae or imported wood or stone.