TL;DR - Remove all non-essential NPC's/Crafting nodes from Cyrodiil to test if that's the issue.
To preface this thread, I personally do not experience the lag issues many do, for the most part. Every once in a while I get the dreaded 999+ Latency problem and the only time I've ever had what I'd consider low FPS was well before 1.6 when I was in a sizable group breaching a keep wall and the moment we crossed the wall's line several Oils came down on top of us, I dropped to 17 FPS for a few seconds. Normally my FPS is 50+ everywhere in Cyro, regardless of what's going on. I'm not going to turn this into what PC, Video card, settings, etc do we all use as there's plenty of those threads already.
Onto my idea that at the very least would be a great test to see what exactly the problem is with many Players having lag that keeps them from an enjoyable PvP experience.
- Remove ALL NPC's that are not part of a Quest hub (Quest givers plus target location) or PvP area (Keeps, Resources, Gates, etc).
- Remove ALL Crafting nodes in overland Cyrodiil, every Runestone, every Clothing node, every Alchemy plant, every Water, every Wood node and every Ore node.
After ZoS removes all nodes and non-essential NPCs from overland Cyrodiil they leave it that way for 1-2 weeks to allow Players to thoroughly test it. ZoS could even make an official post as a
"Call to Cyrodiil Weekend" during that time asking as many Players as possible to jump in and PvP to stress test it. Once the time period is over and the data is in, IF doing the above reduced the lag for the majority then ZoS can start adding in 1 group type at a time until the almighty lag monster starts to creep up again. So maybe they start by adding in just overland Bears, then Wolves (what's left at least), then Mammoths, etc. Once they reintroduce all non-essential NPC's they can then move onto Crafting nodes 1 at a time. This should give them a very good test of what may or may not be causing some folks to lag out while others have little to no issues.
Also, as a side note, I know of 1 way to possibly diversify PvP in Cyrodiil that may at the same time help with lag in overland Cyrodiil. If during this test ZoS decides not to add back overland Crafting nodes, why not add many more to each Delve, since they're instanced anyway. I'd also like to see them increase XP from NPC's in Cyrodiil's Delves (not much, maybe 10-20%). Adding more Crafting nodes to Delves and increasing the XP gain via enemies inside the Delves would open up more opportunities for small group PvP and since they would be instanced from Cyrodiil it wouldn't impact lag there.