SK open and interesting idea, imagine if a company starts making upgrade kits for popular older ratchets.
I think SK is really the only company that can actually make money off the idea
They've been making the same ratchet for what, nearly 80 years without any real changes to the design. I've run into more of them at sales than anything else (sans maybe RP's, but I don't buy those) the sheer amount of them and virtually no change in the design lends well to something like these drop ins.
The only other design as old as the round heads and still fairly common are the plomb/proto pear heads. Even if you double the tooth count on one of those it still is pretty eh compared to 40x2 on a DT80, plus I imagine it would take a lot more engineering to retrofit those as opposed to the drop in mechanism the SK has.
I do think sears could pull it off if the chinese RP's were the same internally as the US ones. I hear they aren't parts interchangeable, if they were I think they really could make some money selling a 72 tooth kit for them (though I hate those damn ratchets).