I'd honestly rather get another short series like Origins than a second Generations series. I liked how Origins was structured since it cut down on the filler material and gave us the biggest moments of the R/G/B storyline. I didn't like that Mega Evolution was used in that series since it didn't make sense in the Kanto setting at the time, but I could ignore that because the pros outweighed the cons. I'd like a spin-off of Origins that follows Hibiki's storyline from G/S/C.
Save One: Gold - covers Gold getting his pokémon and meeting Oak, ends with Falkner Gym Battle
Save Two: Silver - covers meeting Silver, Lake of Rage and Mahogany Town
Save Three: Archer - covers the Radio Tower siege
Save Four: Red - covers Elite Four and Mt. Silver
If they have to push the S&S games/anime back to fix the lack of pokémon, you could probably double it to eight or even more episodes and cover the changes to the Kanto region, like the Lavender Radio Tower, where we can reintroduce the girl from the first series, or Green at Cinnabar Island
Could also squeeze in Eusine's Suicune Stalker Quest, build on the Legendary Gerbils, Ho-Oh, and Lugia, Kimono Girls...
There's a LOT of material from Johto to cover