I presume that UA will do the same thing here as it has done in other situations where it has subbed in an aircraft with F but had only marketed J/Y. That is, only J seats are sold. The F cabin is left empty unless the space is needed. If the F cabin seats are required, UA will assign those to GS and the like and sometimes to people who purchase last minute or otherwise get lucky. But, in any event, it is J service with a nicer seat.

I would be interested to hear the source for the closure of the IAD GFL, but would not be surprised as it simply creates branding problems since it's more than a UC and less than Polaris (at least in terms of bells and whistles).