I think S&W is missing the boat by not offering a wider variety of fixed sight older style revolvers. Not just the "classics", but new models based on the old design. I'd love to see K, L, and N-frame models in all of the available calibers offered with 2-1/2", 3", 4", and 5" barrel lengths. If the barrels were of the tapered variety, similar to the 4" 22-4, all the better.
I know this is a lot to ask, but I think there is a renewed interest (maybe it never left) in the older configuration. I love a good 686 with a 6" barrel, but not every revolver needs to have a full underlug and adjustable sights.
I like the adjustable sights for a target gun, or a primary hunting weapon, but I don't think I will encounter a self-defense situation that merits using a concealed carry handgun at beyond 25 yards. If you can't keep the rounds where they count within 25 yards with a fixed sight revolver, the sights need to be regulated or you need more shooting practice.
Sometimes a company will hit on a classic form that really grabs you in a visceral way. 57chevy, 68mustang, Kbar military knife, Fender Stratocaster, GMC Pacer(just kidding), you get the drift. I think the HD falls into that category. It sorta hits you in an inexplicable way like the shape of a woman does (no offense, ladies). Most of the great larger-framed S&W revolvers are simply derivatives owing a lot of their aesthetic appeal to the basic lines of the HD.
This is my long way of saying I agree whole-heartedly that they should bring back the HD in every possible cartridge.