The transition to APM Team Center as the primary console in APM 10 will definitely be the most valuable feature.
The ATC shows a lot of potential on how we view performance metrics on the front-end and back-end connections in a single view.
An APM tool should have the capability to provide a high-level view of the monitored application and APM 10 is heading in the right direction by just doing that. A single-window view of performance metrics, timeline, applications, alerts and heat maps (DA) throw a lot of data to an engineer in a quick glance.
Another new feature may just have to be Entry Point Discovery. The capability of the agent to detect the application entry point and create custom pbd for this. Interesting concept of automatic discovery and prescriptive change.
CA APM strength is the Custom Instrumentation - just having the capability to capture performance metrics for classes and methods in the application makes this tool a elite candidate.