Cmdlets can have provider-specific parameters, so in this case I would add a registry-provider-specific data type parameter with sensible default behavior to New-Item and Set-Content.

For example...

Set-Content hklm:\software\xyz\abc -value 1

...could create a DWORD value by default based on the type of the value argument, while adding '-DataType String' would enable creating a string value.

Files are raw binary data, but a (BTW unreliable) method to understand what they contain has been in use since years: file extensions.

I can see no reason why in a filesystem-like representation of the Registry you cannot have a value.dwd (which is a DWORD), a value.bin (which is a BINary), value.esz, etc., or at least that is what I would use.