Write Get-Content 'file.txt', put the cursor left of the filename, try to autocomplete the -Path parameter name; it's not in the list.

    # move the cursor to the left of the argument, where the parameter name would be 
    Get-Content 'file.txt'
               ^

    # Write a - and try to autocomplete the -Path parameter name
    Get-Content -{ctrl-space} 'file.txt' 
                 ^
    # -Path is not shown in the list of available parameter names

I don't want all the parameter names shown all the time, removing ones which have been used is really useful .. but if it could show the name for whichever parameter is just right next to the cursor and has been bound positionally, that would also be really useful.

Current workaround for long parameter names - try autocomplete, cancel it, comment out the rest of the line, retry autocomplete, choose the name, uncomment the line.