Jim,
Lots of reasons NOT to:
1-Oxide and slag inclusion(fatigue failure)
2-Impossible to create uniform penetration and fillet shape (fatigue issues)
3-Rapid cooling rate after welding will induce poor base metal microstructure (fatigue issues)
4-Messy process creates lots of spatter and possible arc scars (fatigue issues)
5-Slag removal can be difficult and may create poor paint adhesion.(corrosion)
So in short, if there was ever a process that was NOT suitable for 4130 aircraft welding, FCAW would be it. The ONLY reason mig was ever used in production was for cost reduction, never an engineering advantage. Gas and tig using proper welding process are going to be the best way for you to go.
BTW Jim.....every technology has been investigated at some point or another. Keep the FCAW for welding manure covered agricultural stuff