Update Roadmap re dynamic reconfiguration

Polly-Roadmap.md

@@ -41,13 +41,18 @@ _prototyping started, discussion transitioning to development_
 
 _next after high-priority items_
 
-## Introduce configuration-provider interfaces and/or POCOs
+## Consider introducing configuration-provider interfaces and/or POCOs
 
 Introduce configuration-provider interfaces such as [discussed here](https://github.com/App-vNext/Polly/issues/143#issuecomment-354732829) and [exemplified here](https://github.com/reisenberger/Polly/blob/fa4e8dfb54d79aff480e831a57445978b9205aa4/src/Polly.Shared/CircuitBreaker/IAdvancedCircuitBreakerConfiguration.cs).
 
-### Dynamic reconfiguration during running
+## Dynamic reconfiguration during running
 
-Configuration-provider interfaces would also enable dynamic reconfiguration during running, eg of circuit-breaker thresholds, timeouts etc.  This would make for easier in-production tweaking of systems for stability/optimum operation, especially once metrics/dashboarding expose real-time operation.
+Dynamic reconfiguration during running would make for easier in-production tweaking of systems for stability/optimum operation, especially once metrics/dashboarding expose real-time operation.
+
+Two approaches to dynamic reconfiguration have been considered:
+
+1. Introduce the **configuration-provider interfaces** described above.  Policies could then become dynamically reconfigurable by coding configuration providers backed by updatable configuration sources, as [discussed here](https://github.com/App-vNext/Polly/issues/143#issuecomment-354732829).  _Note:_ This leads to **mutable policy instances**. Questions arise then such as how to ensure updates of configuration are atomic; and the effect of dynamic reconfiguration on executions mid-flight at the time of update.
+2.  (_already available_). Treat [PolicyRegistry](PolicyRegistry) as a [dynamic store of policies](Dynamic-reconfiguration-during-running).  Pull policies from the registry at call sites. Use events to update policies in the registry on a change in the underlying configuration source.  _Note:_ With this approach individual **policy instances remain immutable.**
 
 ## Refresh syntax to reduce the number of overloads