I don't mind another powerful item to boost fire rate in the game. However, the high tier items usually have some special effects or conditions to use. I want to say that item itself is boring.
Also, we already have item, that able to give almost the same stats — Burst Fire. With items, its effect can be everlasting. But the main thing is the price. It's twice as cheap.
In my opinion, we can take the concept of Burst Fire and reverse it. An instant, but short-living or gradual, but constant (cough, McGinnis's M1, cough). There's already a plenty of suggestions of Intensifying Magazines, but with the fire rate instead.