The XM556 Microgun, a handheld minigun, could be the firearm that would check every mark on your wish list.
The XM556 was designed by Empty Shell LLC, self described as “one guy over the last two and a half years with no training, no college, just a GED”. The XM556 was designed and engineered around the 5.56mm NATO cartridge which helps with the small design. The current Microgun is significantly smaller and lighter than it's larger counterpart, the M134, but still fills the same role of suppressive fire and does so without the weight or larger footprint of the M134.
The XM556 was designed from the ground up as a new weapons system with parts that are unique to the Microgun. Although it looks and operates like the M134 on the outside, there was a new bolt style that was conceived and designed to eliminate current known issues with the M134.
The Microgun is sixteen pounds and rated to fire four thousand rounds-per-minute. The XM556 is fully functional, but the downside to civilian firearm owners it will be unavailable to the civilian populace. In Canada it will be a prohibited fully automatic firearm, and in the US thanks to the 1986 ban on newly manufactured machine guns it will be available only to military, police, and class 3 Federal Firearms Licensees (FFLs).
Although it will only largely be available to be fired by civilians at licensed class 3 gun ranges when commercially available, this is a firearm that is on our wish list and likely on many other firearm owners as well.