I would say yes, but I feel like the beauty of the forerunners is that they're so mysterious when it comes to the games. The less we know about them regarding the games the better (in my opinion) But whatever I'd probably still play that hypothetical game. The only problem is that Halo's combat loop with the different aliens is so spot on that haveing a game with just an entirely different enemy would be difficult to make successful.
Nope. I have zero interest in the forerunners or ancient humans after Halo 4 and Halo 5. The mystery of not knowing who or what they were and how they could build such massive structures was what made them interesting in my opinion.
It would be interesting to see what they could do with it, but it would be a huge change from the halo game norm and wading into dangerous waters considering the difference in technology between modern humans and more advanced ancient humans and forerunners.