Maybe this is more of a bug than an "idea", but something that might warrant looking into.
I added subtypes to our Points and Connection Lines, in order to enforce certain domains and attribute rules. When I add the fabric service to a new map, it brings in the Point and Connection Line subtype group layers, but with no subtype layers in them.

I can use the Add Preset → Subtype Group Layer tool to bring it in after, but certain Parcel Fabric tools, such as "Merge Points", will not recognize the subtype group layers as a valid points layer.
For now, I have been adding the Points and Connection Lines layers as regular layers, then symbolizing by the subtype field, and everything seems to work as expected that way.
I understand that something like Merge Points won't work across two separate TOC entries, so the subtypes will always be a problem there, but perhaps at least getting the subtypes to come in on the initial import of the fabric? Or to ignore the subtype and bring it in as a standard layer? Anything but the empty layer I'm getting now.