How about something that is SMG-friendly, or pistol-friendly? The EM-2 was at 3.4 kg - empty? Add almost 1kg for a full magazine, and we're at 4.4 kg, or about 10 lbs.
The 'new-age' carbine or SMG could still offer an useful firepower, but in a smaller/shorter package and lower weight. The M2A1...