I'd be shocked if there's no Halo 3 anniversary. I saw what Stinkles said, but still. Halo Wars 1 is being remastered despite being BC, and is getting absolutely zero advertisement, talk about diminishing returns - so if that's happening I'm pretty sure Halo 3 will be.
I mean Halo 3 was massive and MCC was broken. Not to mention it'd come out around the time of Scorpio, Halo 3 with upgraded graphics and in 4K would sell decently especially since it won't be broken AND there will be a PC version this time. I'll believe there's no Halo 3 Anniversary once E3 2017 is finished.