I’m just a normal avid biker...so just speculating with some common sense.
Shimano motor backward compatible in old frame...that would be awesome...but very hard to believe.
I would not be surprised if YT would launch a more trail like ebike, shorter travel...
Anyway...we will not know until...
Most likely YT will have a complete new decoy in 2021 with new shimano 9000 motor. Which will come with the 700W battery.
Don't think they will release a 700W batt for the current version...