I think there would be more cons than pros with a 45 Shield.
The size and handling chacteristics with the 9mm and the.40, seem to work out pretty well,but I see a 45 version as too much of a good thing,and there is no way to keep the overall size as compact as the 9 and 40.
I don't know why anyone would even want one for what you'd give up,but that's just me.

ETA:What I'd really like to see is a nice .22 LR Shield for same size gun training on the cheap,and it would be a nice pest gun too.

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Blessed be the Lord,my Rock