That’s almost exactly what it was. The 224 sold poorly while the 229 sells very well. Sig took the slide from the 224 along with the 224s take down lever, slide release and decocker and made a new SKU. They did something similar back in the early 2000s with the P228R. They had a lot of slides but at that time had stopped making the classic non-railed frames so they put those uppers on 229R frames and called it the 228R until they sold out of those 228 uppers. Back then people just didn’t spend the money to bling out their pistols. So when they had excess parts they’d cobble together a working firearm it they typically sold well to collectors. I doubt we’ll see Sig do this anymore since people buy slides readily and Sig of today sells tons of small parts to customize your gun.
The 224 was a neat idea that just came at the wrong time. People back then had an aversion to aluminum and steel framed guns where nowadays those guns are in high demand to the point you have companies like S&W making metal versions of their polymer pistols. It’s interesting to see how the industry has shifted for the past 30+ years. We’ve basically come full circle.