Each class would have the Threadweaving class feature, which allows it to access Threadweaving rituals. You'd have to perfom a Threadweaving ritual to connect to a new facet of the item or a new item. The different powers of an item would be keyed to the success of the ritual's skill roll.
But wasn't there a limitation in ED about the number of threads a character could have active?
IIRC, the limit was one thread per rank in the Threadweaving talent. Threadweaving was also used by spellcasters to power their spells.
Another big issue with ED magic items was that you had to learn stuff about it in order to awaken the higher-level powers. I think you always needed to learn the item's Name (Names are a big thing in ED, as evidenced by the eight PC races collectively being known as "namegivers") to get the first powers, but later you needed to learn of various events in the item's history, previous owners, who created it, and so on. You could also relive the item's legend in order to gain bonus XP to spend on awakening more powers. E.g. if the original owner had perished fighting a certain horror, one of the item's high-level deeds would probably be killing said horror.
As Earthdawn was always very D&D like, where they explained typical stuff like Dungeons*, Monsters**, limited Spellselection*** and magical Heroes**** quite logical .. it is only fit that they finally make a version for D&D since 4E went in the direction they have gone.
Exactly. When I first looked at Earthdawn, I thought "This is like D&D, only with logical reasons." People built magical underground shelters to hide from the Horrors, many failed, and can be looted by enterprising characters (though the horrors might still be there). You become supernaturally powerful eventually, because you're infusing yourself with magic. Spellcasters wear robes, because at the beginning of the scourge they wove their spell matrices into them and now it's tradition.
You have classes and levels (disciplines and circles), but they work in reverse. Your discipline gives you access to certain talents (early ones tend to be magic-boosted skills, with higher-level ones being more overtly magical). You spend XP to increase their power, and when you're good enough you can advance to the next circle in your discipline, which gives you access to two or three new talents.
It also has an interesting way of balancing races. In the game, there is something called Karma, which can be used to enhance certain talents. Some talents require you to spend Karma, while it's optional for others (depending on your discipline). You buy Karma by spending XP, and for the more powerful races (like Obsidimen and Trolls), it's more expensive than for others, and they also gain less benefit (an Obsidiman adds +D4 to the roll when they spend karma and pays maybe 10 XP for it, while a windling adds +D10 and spends maybe 5 XP). This means that more powerful races advance slower.
Like in 3e, there are no class limits based on race, but of course certain races are more suited to certain classes (you won't see many windling warriors).