I believe all the OP is asking for is when you open an image into Photoshop from ACR, two layers are produced, the first or lower layer the image with ACR defaults, and the second or top is the layer with the current ACR settings.
The way it works, now, is one layer, with the current settings, is available when you open into PS.
There might be a way to use a smart object, as you describe, to accomplish the OP's dual-layer situation:
Open a raw image in ACR, then without changing anything,
Press Shift / Open Object to open the image with default ACR settings as a smart object into PS, then Ctrl-Shift-Alt (or Cmd / Shift / Opt on Mac) N E. The creates a new blank layer and rasterizes the lower layer into it.
Drag the rasterized layer below the smart object layer in the layer pallet.
Now to adjust in ACR, double-click the smart-object's thumbnail to open in ACR and make the adjustments.
One note is that you cannot just duplicate the smart object layer because each will point back to the same raw file and the same XMP file with adjustments rather than be independent layers with their own adjustments.
Besides just creating a default-settings layer below the smart-object layer, you could click into the smart-object, click Auto tone, then exit out, then Ctrl-Shift-Alt N E the auto-settings into another raster layer, drag it below, then click back into the smart-object, and reset it back to defaults or leave it at Auto and do more adjustments.
I think if I was doing this, i.e. opening the default and an adjusted image into PS as layers, I start with Lightroom, which has the same settings as ACR, make some adjustments, and if I wanted to have the original settings as a layer, make a virtual copy, reset it's settings so it'd have the ACR-default settings, then select both the original and virtual copy and choose Open as Layers into PS, or whatever the right-click option is called. Neither layer would be an adjustable-raw, anymore, just a rasterized image, but this is the same as the OP's scenario.
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