That setting has been missing in all of the Beta's.
I first noticed in public beta 1 when I plugged in my earbuds and the Music App was not suggested.
Public beta. 4 now and it's still missing.
I should imagine it will be reintroduced in a later Beta.
EDIT.
In fact I have just checked and the setting Handoff & Suggested Apps has now changed to just Handoff so maybe it is hidden somewhere else.