Look what happened to the S&W 3rd generation all steel combat pistols. They were replaced by the M&P polymers. It took about 4 hours to forge the frame of a 3rd generation versus 45 minutes for polymer M&P frame. It's a matter of business reality of cost vs supply and demand. I doubt if Sig USA will pick up the lost business of all steel pistols now abandoned by Sig Germany....
The question Sig USA would have to answer is what is the USA market for a production P220/226 all steel 5" and 6" guns. If that were seen to be profitable then they might go after the X version sales. Craftsmanship is a separate issue.
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Look at Sig USA's 2020 line-up in which they have eliminated all non-Legion 220's and 226's. We're talking aluminum frames, and is much cheaper to forge than steel.
A Sig USA all-steel pistol (competition or combat) is DOA.