One of the things I miss most about second edition is the simple rules for creating magic, or daemonic items. I have an idea in my head for a campaign where the players come into possession of a daemon weapon, which is being sought after by a chaos warlord wanting to name himself the high warlord and lead the armies of chaos against the Empire. Is this possible in the new edition? I want the weapon to have power that would be tempting, but eventually lead to the ruin of the user by corrupting them.

Point me in the right direction if you're able. I may have just missed something.

One magic item variation they've done is giving the bonus for superior item (1 fortune die bonus), with the added effect that fortune points spent using it give expertise dice (yellow) rather than fortune dice. That's a pretty significant boost.

you could modify the "profane weapon" from the gm's toolkit. combine it with corruption rules from winds of magic, give it some other cool power that would make people want to use it despite the risk.

Don't have WoM yet. Hoping it'll be in at my FLGS this week.

Using the Profane Weapon style object as a base (or just a Superior Weapon if it's too powerful for a new group) and adding a "Gain 1 Corruption each time you kill something" type property should do the trick

The bearer will soon fall into Chaos workship unless you (the gm) often consumes Corruption points to add difficulty dice to his actions (see the news Winds of Magic and Corruption )

To make it very tempting to keep for the players, you can add anything they would fall for : higher base stats (like the Profane Weapon), a Special Power like "Your Strength increase by 1 once the blade is covered in fresh blood (temporary for the Encounter)", or "You (re)gain one Wound each time you kill (or hurt) someone with the weapon", etc.

An attractive bonus that a Witch Hunter, a fervent Zealot or a Priest would condemn if he understands what the weapon does (a Mage too if he is on "the right side") -> You may have to keep the properties secret until activated and only tell the bearer of the weapon. Other players would have to make Observation / Intuition / whatever checks to start seeing some unatural things, depending on the group composition