Are you wanting to flash an R1 MESSAGING to an R8?
Or flash the ACS to R8?
For the ACS, you must be an R7 to be able to flash to R8 (different hardware)
For the Messaging, R8 hasn't been released yet, but since you can flash R1 and R6 to R7, they will probably have a path to go to R8 when it hits.