I can definitely see a Firefight map pack coming sometime. There already is a Crater remake (the club from New Alexandria), and Lost Platoon would probably be another favorite to bring back.
Yes, in my opinion none of the firefight maps are made for long lasting games that we had in ODST. More firefight maps are defiantly needed, and I'm not sure why we can't firefight on forged maps.
Kind of. Although it would only really work if they implemented a "classic firefight" playlist where you could play through continuous waves, rounds and sets until you had consumed all of your lives.