I think there would be more interest in regular mags with a higher capacity, 7 or 8 rounds. They would be easier to manufacture and would fit in mag pouches. Nothing against the drums but it seams like they would be more expensive, bulkier and heavier.
A double stack mag would be the best option.
+1, 7 or 8 round magazines make more sense to me too.
How about creating a +2 magazine extension that fit on regular mags, it would be easier to design/make then a completely new drum.