It most likely won't be avaliable for the s8 or s9. They usually only use their most recent S flagship to participate in the beta. It is unknown if the S8 series or Note 8 will even get Android 10 because it has already had 2 major software updates
History says put a fork in it for S8 other than maybe a quarterly non-timely security update, but dreams are good so keep up the positive thoghts. My thoughts regarding Samsung update policies were negative enough to help drive me to camp Apple.