[EME] To what extent should EME support usage rules?

Now expiration time is the only usage rule EME API supports by Bug 25537<https://www.w3.org/Bugs/Public/show_bug.cgi?id=25537>.

Is the expiration time sufficient for the envisioned use cases? or
Is there still the room to add other parameters?

For instance, in case of rental video, start time and period after first use are used in general.
In this case, constructing UI only by expiration date might be confusing to users because end time shortens after first use implicitly.
As to start time, it might be useful if video is upcoming movie; i.e. start time is future time.

Honestly, I'm not sure what is the criteria to decide which usage rules are common concept in EME world.
Any opinion?

Thanks,
Shinya