This is the first I've heard that. Is it confirmed, or just speculation?
I don't think it's any of the above, rather dreaming out loud.
I'd be surprised if it happened given their current quasi hiatus status.
Having said that, the Winter Carnival last month were a blast! They're one of the few bands I personally wouldn't mind seeing with Furthur. If I recall correctly, the cheese / dog co-bill in 2006 had Ratdog opening cheese getting two sets ... so could easily work if reversed in the case of furthur.
Well said, my friend. SCI definitely needs to get back to national touring regularly.
As a matter of fact, here are a few youtube clips of SCI from Winter Carnival 2011: www.jambands.com/the-loop/2011/03/12/sci-s-winter-carnival-2011
SCI + Ratdog show at Red Rocks 7/1-2/2006. From SCI's wikipedia page.. "They recommenced in the summer of  to play several co-headlining shows with Bob Weir's Ratdog including a sold-out two-night run at Red Rocks in Morrison, Colorado".
Here's the playlist from those two shows, and below is a link to the audience recording of String Cheese Incident Live at Red Rocks Amphitheater on 2006-07-01 (July 1, 2006):
Banter > One Step Closer
Got what He Wanted >
Mrs. Browns Tea House
Can't Stop Now >
Kidney in a Cooler*
Way Back Home
China Cat Sunflower^ >
I Know you Rider ^
* w/ Keller Williams (guitar, vocals) & Lou Gosain (background vocals)
^ w/ Keller Williams and Bob Weir, Jay Lane, Kenny Brooks and Jeff Chimenti of Ratdog
Audience Recording of String Cheese Incident Live at Red Rocks Amphitheater on 2006-07-01 (July 1, 2006): www.archive.org/details/sci2006-07-01
Here's the set list for String Cheese Incident Live at Red Rocks Amphitheatre on 2006-07-02 (July 2, 2006):
Set 1: Outside Inside > Best Feeling > Sittin' On Top Of The World, Gonna Move Up The Country (Paint My Mailbox Blues), Stagger Lee, Peace of Mine, Black & White, Search, Shooting Star
Set 2: Going Down The Road Feeling Bad, It Is What It Is, Sometimes a River, Smile, Eye Know Why , Rivertrance
Encore: Tamba, Black Clouds
Here's the audience recording for String Cheese Incident Live at Red Rocks Amphitheatre on 2006-07-02 (July 2, 2006):
More music takes you Furthur, guys. There's no reason not to give music that is new to you a try. +1 to Bob Weir for recognizing their brotherhood with the greater Grateful Dead Family. Bob's as open minded about music as Phil these days. And to be honest, that is not at all surprising to me, as I've previously said in other threads. Too many people here seem to just like one flavor (but fortunately, not all, and God bless you all).