Ah! You’re trying to build a better water heater! Bravo! Unfortunately, the big makers don’t WANT a better water heater. I can’t completely fault them. It would take a lot of will to drive oneself out of business and cause all one’s employees to lose their jobs.
I’ve seen already from the other post that you’re a lot more technical than I am. Larry Weingarten can probably match you, but I can only answer as best I can.
I’m not sure what you mean by passivating the sidewall. A steel tank is already mostly lined with “glass,” which approximately does the same thing.
We prefer ball valves to gate valves. I’ve had ball valves fail on me, but not as often.
I think having two anode ports would be superior, but that’s not how they do it. Putting it in the hot port does constrict flow. It may be a matter of, “we’ve always done it this way.” Can’t say for sure.