I tried different combinations on my both Kobo Forma and KA1, however, didn't get multiple-fonts works as expected.
this feature broken since after version 4.31.19086. some of screenshot attached, before it works, the poem part shows Kaiti property, but whows Heiti in new firmwares.
attached sample kepub file(its Traditional Chinese content, please ignore if you can not read Chinse
).
--Thanks