One point that have been raised was a chance of abuse in case of Flaming/Frost/Shocking... weapon. In the case of the flaming dagger, giving the Fire keyword to all your powers. That would allow:
- Sorcerers to ignore 5/10/15 to all his powers (he is not forced to take only power already with fire keyword).
- Dragonborn arcane character give him +1/+2/+3 to hit with all powers (because taking Draconic Spellcaster become a no brainer, and you can be quite sure his breath will be fire).
- Tiefling get +1 to hit/damage (Hellfire blood)
And that's are the one I can think of at the moment, and I surely miss more.
But now, you see there is a staff that do the almost the same, instead of having a daily, it allow you to switch to Acid (nice for our Dragonborn Dragon Sorcerer with Admixture Breath Fire/Acid), so that's one less point to concern about I think.
Also, the staff explicitly express it can be use only as an implement, it just disallow to us his power with a Weapon keyword power, even if a staff can be use as a quatterstaff.