You're gonna be waiting for quite some time. I'm making steady progress, but I still give it about two years.
Also, too late for story modifications. It's already been scripted and voice acted. I thought about making the story continue from the SE rocket, but I already used elements of SS3 and SS4 (some lore pieces, enemies, weapons), plus I needed to explain away the holy grail. But it's not like Sam games aren't already full of wacky time stuff, so a needlessly complicated backstory is on brand for the series, I feel.