Observable feature flag values

I just watched ASP.NET Community Standup from May 21st and I really like the idea to have standardized API for feature flags.

In our system we have backend services that don't expose any HTTP API but perform some asynchronous processing or execute tasks on schedule. And it is useful for us to have a notification mechanism for when feature flag value changes. For instance to enable or disable events stream consumer.

In our custom implementation we use RX and expose both synchronous and observable methods to retrieve feature value. Would be nice to have similar possibilities to observe changes of feature flag values in the API that you guys develop.