Now busy, busy parents can't even find the time to mollycoddle their little darlings themselves.

I hope it's expensive.

Maybe developers will create/port plugins replicating the functionality of Firefox extensions for Chrome, but what about ad blocking?
One of the key reasons I use Firefox is to view the web without any adverts – any adverts at all, and that very much includes Google AdWords/AdSense.  What are the chances of that being possible in Google's own browser?

The multi-threaded approach* and improved javascript handling seem to be good solutions... to problems I haven't encountered.  I know Firefox has (had) a reputation as a memory hog but I genuinely haven't noticed a problem even once, and I very rarely experience browser crashes; even when I do, I regard them as utterly trivial, barely even an annoyance.  Hence, I don't find such performance refinements particularly compelling.

I'm less neutral about the GUI: my initial impression is negative.
The argument is made that since the tab is the primary operating unit in the way people use a browser, the array of tabs should go across the very top of the window, above the menu and address bar; in effect, this gives each tab its own menu/address bar.  My view is that the standard layout is more usable, for precisely the same reason: the tab bar is the next-most-important element after the body a web page, so I want a tab bar directly adjacent to the browser pane, without a menu/address bar interposed.  We'll have to see, but I think a change would be a design error, which only makes theoretical sense when over-intellectualised or when seeking change for change's sake.
It seems it'll be possible to omit the menu/address bar altogether in some cases (such as when accessing Gmail), but that's not really what I want either.

As I've mentioned, I don't like autocomplete functionality, particularly on shared computers, so the new GUI's focus on integrating past web activities into the address bar and a dynamically-generated default/home page would be something I'd want to disable completely, immediately.  I think that'd be possible via a 'privacy mode', in which browsing activity isn't saved for future customisation or display.  That might address my concern, if it can be set as the default rather than a 'per-tab, per-instance' setting.

The 'sandbox' model of security, whereby any malware process would be confined to a single infected tab (apart from those using third-party plugins), looks promising, but I don't know anything like enough about the topic to really comment.

A theme running through the comic strip is that most features and the overall architecture are open source and/or available as web apps to other developers, including developers of other web browsers.  The implication is that Google want to redesign the web itself, and web browsers as a class of software, rather than merely produce another browser: to define a new baseline rather than just add their own product to the existing market.  A baseline and developers' mindset which favours Google, of course, but that's only to be expected; they're not a charity.

So.  I'm interested, but my main hope is that Mozilla are more interested, and this kick-starts a partial revision of Firefox – I'm no Firefox fanboy, but I'm still more likely to follow that route than switch to Chrome.

*: I know; threads aren't processes, so 'threaded' is technically the wrong term, but it's more readable in this context, okay?