I always though there is something off about those defaults.
Hopefully Google guidelines are backed by some real science.

My only concern is the impact on $container-max-widths:

• md: 900 » 787.5
• lg: 1200 » 1073.4375
• xl: 1800 » 1448.4375
• xxl: 2400 » 2004.375

With rounding down to nearest 100px we would get: 700, 1000, 1400, 2000

100 * math.floor(map.get($grid-breakpoints, 'md') * 0.009375)
// or with math.div() to make it more obvious:
// 100 * math.floor(math.div(map.get($grid-breakpoints, 'md') * 0.9375, 100))

My biggest problem with the current ones is that they exactly match common screen resolutions (especially xl and xxl). Any sort of sidebar like edge's or firefox vertical tabs bumps you down a breakpoint for no real reason.

$container-max-widths

Yeah that seems better actually. Many screen sizes will still get a wider container with that change eg. 1080p goes from 1200 to 1400px.

We could actually use container queries now, any thoughts on these questions? #18983 (comment)

sidebar like edge's or firefox vertical tabs bumps you down a breakpoint

I think that ~55px margin is going to be perfect to account for this.

@KaelWD Does this change mean that a Vuetify v3 responsive application will potentially have to re-test and modify every page's layout?

Is there a way to revert to the v3 breakpoints, other than by overriding the $grid-breakpoints properties in _variables.scss?

Does this change mean that a Vuetify v3 responsive application will potentially have to re-test and modify every page's layout?

yes

Is there a way to revert to the v3 breakpoints, other than by overriding the $grid-breakpoints properties in _variables.scss?

If you are not using Sass, you would need to append custom CSS for .v-container, .hidden-*utilities + a bit more to patch VTabs and VBottomSheet.

If you are not using Sass

@J-Sek If I am using Sass, is there an easier way to revert to the v3 behaviour?

I've added instructions to the upgrade guide with changes needed to keep the v3 values.