Bit late to this, but went back and listened to most of the R1 Big Weekend.
I like plotting out when the presenters come and go, and who's driving the desk etc..
Some of the specialist presenters missing were Alyx H, Kenny Allstar, Daniel P.C, and is Shanequa even with Life Hacks any longer, but was not there either.
Driving the desk (from what it sounded like)
FRI: Ricky, Matt, Sam, Danny, Jack
SAT: Ricky, Sam, Matt, Jack, Sian
SUN: Charlie H, Greg, Lauren Layfield, Arielle, Danny, Sian
On R1Dance, FRI & SUN: Conor Coates; SAT: Martha
Most of the main DJs on 2 to 3 days. 1 day appearances for Charlie T, Pete T, Benji B, Lauren Redfearn, Minah (does that count), Swarzy, Jessica I.