Truth to tell, I am little bit of a Caton-Woodville with my 1/72 armies: the most sincere efforts to be historically accurate can be trumped by artistic license. In this case, I want my hussars and RHA in Home Service order; or, HSO braided attilas with bedford cords and sun helmets/pillboxes. More in the style of the early/mid-1870's, perhaps.
Colonial Volunteers are not a unworthy subject. I just think it is a shame HaT could not have done something like their Swedish Cavalry set. FLH, Durban Mounted Rifles, Natal Carbiniers, Natal Mounted Police, et c, all in one big box.
To make the set you propose adaptable as hussars or RHA would take only the inclusion of sabers. They needn't be attached to the figures. I would propose the weapons be separate to give the modeler the option to attach the ones he wants. Make most of the figures with peg-arms, and offer a wide range of arm options: carbine, pistol, saber, hunting knife, whip. Add an assortment of heads as well, wearing alternate sun helmets, pillbox hats, forage caps, et c.
Please understand, old friend, I am not opposed to your suggestion. I am in favor of improving upon it. Make it a set with enough extra heads and arms, and I am on board 100%.