Mitakeumi's sanyaku position is 90% safe. The last time a non-haridashi sekiwake went 7-8 and was demoted to hiramaku happened after Hatsu 1992, when both Takatoriki and Kotonishiki were demoted to give way to Akebono and Takahanada. http://sumodb.sumogames.de/Query.aspx?show_form=0&form1_rank=S&form1_wins=7&form1_losses=8&offset=50 query, http://sumodb.sumogames.de/Banzuke.aspx?b=199201 banzuke for Hatsu 1992.
My guess for Natsu 2018 sanyaku:
Tochinoshin (100%), Ichinojo (90%)/Kaisei (10%) S
Mitakeumi (90%)/Ichinojo (10%), Kaisei (60%)/Endo (39,9%)/Abi (0,1%) K