I can only speculate on the SJ'ing as i'm not up on the Dressage or Eventing scene, but I think subjec to horses staying sound then Michael and John Whitaker are certain of a place, then perm any 2 from Ellen Whitaker, Will Funnell, Nick Skelton and David McPherson.
Tim Stockdale is out of the running as Corlato is injured and Robert Smith has no form to speak of this year. I think Nick and Arko will be outsiders for a place unless Arko proves himself at the highest level again very quickly, although he does have Russell as a fallback if necessary and his experience is second to none.
I'll stick my neck out and say Ellen and David for the last two places