What they mean by "change the damage calculations of tanks"?

[Rbstr]

Changing to a VIT modifier doesn't change anything from their perspective, it only make things easier for players. I think SE is struggling right now with raid design because they can't predict and account for tank DPS. How could you when aggressive tanks are pushing 800+ per raid and timid tanks stay at ~400-500? The range is so wide, my guess is they want to narrow that gap.

I agree on this point. What they want to do is make it predictable.

but I don't agree here at all.

Simplest and easiest way to do that is just throw a hard cap on tank's STR scaling. No I'm not vouching for it, I don't want to see a change like that.. But frankly what else would provide results of significant change.

You forget about how arbitrary issues of DPS really are in balance. It's about ratios rather than absolute magnitudes.
500dps into 1000hp is the same as 2dps into 4hp.
Tanks doing 600dps vs DPS that do 1000dps is the same as Tanks doing 6000 and DPS doing 10000.

You have one caveat in that if tank damage approaches DPS-class damage close enough you might obsolete the DPS classes.
Otherwise the actual number the tank puts out are irrelevant as long as they are predictable.
If damage is consistent all the devs have to do is adjust HP values/dps checks with that in mind.

The best way to get it to flatten out is to just make it so stats scale like all of the other classes: Make the class care only about one primary stat and give it the other one for "free". For DPS that's mind/int/str/dex to care about and the vit on the left side with the ability to need on the correct primary stat gear. So for tanks that can either be putting strength on fending accessories instead of vit or changing their damage stat to vit. Both of those things sort it out automatically. Or even inventing a new stat to slap on instead of strength and putting that on fending accessories.
Everything else is just using the newly predictable dps numbers for future content balance (Because those options wouldn't actually change any previous content. We already had strength tanks doing that stuff!)

edit: You could also role lock accessories and thus limit tanks to vit stuff. But that's a wholesale nerf to damage and those are rarely ever good options.