The Russians seem to be sold on the general concept, producing a version of the Saiga 410 equipped with military AK-style furniture: folding stock, pistol grip, 10rd magazine, et al. (All of the nasty bits, short of a bayonet lug, which would prevent US importation.)
Back around the mid-1980s, Franchi experimented with a select-fire bullpup .410 which vaguely resembled the FN P90 (with the exception of magazine placement and sights). It used a 15rd box magazine and fired 200rpm on full-auto.
For defensive loads, there are three-pellet 000 Buck .410 shells (2.5" Hull) available from American Deringer (made by Winchester) and Sellier & Bellot. S&B also offers a five-pellet 00 Buck loadings in a 3" .410 hull.
Experimenters have even surpassed the pellet count of the S&B loads. In the Handloader's Digest, 11th Ed., C. Rodney James wrote up his experiments with six-pellet 00 Buck .410s. Furthermore, in Cartridges of the World, 6th Ed., Frank C. Barnes mentions playing with five-pellet 000 Buck loads. These were launched with either 16 grains of 4227 or 14.6 grs of 2400 to achieve a muzzle velocity of 1,100 fps. He claimed patterns of ~6 inches at 25 yards.
Playing with ball diameters other than standard buckshot, I have calculated that a 3-inch .410 hull could hold either five 93gr .395" balls or four 104gr .410" balls. (The former is calculated from the length of a six-pellet 00 stack, and the latter from the length of a five-pellet 00 stack.) The .395" ball is available for muzzleloading rifles from sources such as Hornady, while NEI offers a .410" ball mold. Given the straight stack of the pellets, a rifled choke might actually enhance the patterning...shades of the Paradox shotguns!
Even if you didn't want to play with pellets this large, you could try substituting the soft lead pellets in the S&B loads with 'premium' buckshot (hardened and plated), commercially available from Ballistic Products. Ballistic Products also makes a nifty '0000' Buck, a true .380" pellet.
