As I understand, most of the lag problems come from the fact that calculations are done server-side, and that over the time it became too much of a burden for said servers. I acknowledge that if they were done client-side, it would give players the opportunity to cheat, as we saw in the past. That being said, I would argue that many calculations could indeed be done client-side, with a server-side random counter-check once in a while to make sure said client isn't editing memory.

Let me take a quick example:
You're a Pact [obviously] templar, running around Cyrodiil, looking for foes, alone and epic. You encounter a dozen AD [you know how they move in packs] turning some resource. Confident, you buff up, jump on top of them with an explosive charge, turn evil, crescent sweep, and spam those jabs. Jabs-jabs-jabs.
For each jab, the server has to calculate the base damage based on your skill's level, mitigated by your attributes, mundus, equipment, the various effects of your armor/weapon/jewelry sets, a dozen bonuses coming from champion points and so on, and then for each yellow player hit, said damage mitigated by their equipment, champion points, and so on.
Scenario 1: all calculations are done server-side, multiply that by a lot of players, the servers die of exhaustion, you get lag [today's situation]
Scenario 2: many calculations are done client-side, you're a naughty cheater, you make your ultimate hit for 120k, obliterate the whole gaggle in one sweep, display a smug and stupid face, bring dishonor on the Pact, get banned from said Pact, one of the calculations got randomly counter-checked by the server, which raises the discrepancy, and you get kicked and/or banned from the game.
Scenario 3: many calculations are done client-side, no one is cheating, a few of those calculations are counter-checked by the server, the numbers check out, you manage to heroically decimate two or three bananas before getting overwhelmed and die an epic and tragic death, the Pact honors your memory, and your brother your wife. For the Pact!

Limitation: this example shows that with a lot of luck on the cheater's side, the server could have missed the 120k damage sweep, depending on the tweaking of what portion of the calculations are counter-checked by the servers. While this is true, who in their right mind would risk seeing their account, in which they poured hundreds or thousands of hours of their life, banned for the tiny chance of getting away with a couple shenanigans?

The lag problem has been acknowledged by the team, and week long tests have been planned. This would be the perfect time to think about the kind of solution I humbly suggest.

Obviously I have no knowledge of the game's codebase, but it seems to me like a pretty cheap way of cutting down most if not all of the lag with pretty much zero cost (not having to purchase expensive hardware, very low development cost). I would love to receive feedback from the developers about this idea.

Thank you for reading.