Ebata's absence is not a real problem for me tbh. Back in OGQ 2012, Nana Iwasaka and Kanako Horai were presented instead of Ai Otomo and Kaori Inoue. Yet the latter made it into London. So Ebata will defly go to Rio, and probably Uchisato as well tho we don't like her at all lol. About Risa, i read somewhere that she refuses to participate in national team for the time being so it's very unlikely for us to see her again in Rio.
The MB line up for Japan this year seems to be fixed already with Araki, Yamaguchi and Shimmamura.
Tashiro as the second setter is still a questionable choice tho.