Darkside Chronicles is a rail shooter remake of 2 and CV. There's not going to be really any new plot in that one.
Well, from what we've seen so far Darkside Chronicles will be (yet again) a remake of Resident Evil 2 and CV, although that's all we've seen and that is all Capcom are willing to release at this point. Remember that when Umbrella Chronicles was released, Capcom simply stated that it was a remake of Resident Evil 1 and 3, and gave no mention of 4th Survivor, Rebecca and Richard's story, Wesker's multiple storys, and finally what happened 2 years before Resident Evil 4 (Russia).
Personally, I can see Darkside Chronicles having a story involving breaking in to the Spencer Mansion as seen in Resident Evil 5, we didn't see anything else of that mansion except from outside of the main room and inside the grand hall. Then we don't know what happened to Chris after Jill and Wesker went out of the window, I'll take a hunch that Spencer could mutate in to a Tyrant, afterall he is one of the founding members of Umbrella that seemingly wasn't injected with any virus.
But Resident Evil 5, I'm playing through it again, this time on amateur to collect all of the emblems, and I'm playing co-op on professional with my friend, and I'm still blown away by it. Granted it doesn't feel like the old Resident Evil games, there isn't much exploration and not much puzzle solving, and the AI seems sometimes worse than Resident Evil Zero, but in a way it still does feel like a Resident Evil game.
It's a shame that Capcom are adament that Resident Evil 6 will be a complete re-boot of the franchise.