I'm also thinking Sothe will have lord status but gain auto-kill ability when he promotes. If this is so, he'll make one of the most interesting lords yet.
Also, I support the idea of assassin through self training; the Fell Contract was somewhat pointless in FE7 as Matthew/Legault had already basically signed their lives away to Eliwood's army. In FE8, the Ocean Seal was useless because a) The item has no connection to assassination, and b) Given the choice between making Ross a berserker and Colm an Assassin, I will unfailingly go with Ross. Colm is useless in the game after Rennac is recruited anyway.