docs: capture PD future-state architecture

docs/servers/PLAUSIBLEDENABILITY.md

@@ -2,6 +2,8 @@
 
 Primary Docker host running all production workloads.
 
+> Planned direction: this host remains bare-metal TrueNAS Scale and becomes the long-term primary production platform after the HL15 Beast rebuild. See `docs/planning/PD_FUTURE_STATE_ARCHITECTURE.md`.
+
 ## Specs
 - **OS:** TrueNAS Scale 25.10.2.1
 - **CPU:** Ryzen 9 3950X
@@ -76,3 +78,12 @@ Current light-tier notes:
 ## Pending
 - Add Pangolin resource + DNS for `ai.paccoco.com`
 - Install fresh editor
+
+## Planned future role
+- Primary NAS after Serenity retirement
+- Primary production Docker/app host
+- Primary shared database host
+- Primary media / automation / identity / monitoring host
+- Primary Technitium source node
+- Future home of qBittorrent + ARR after storage ownership moves local to PD
+- Acceptable host for tightly segmented cybersecurity VMs, but not an unrestricted lab/free-for-all hypervisor